LM2574x SIMPLE SWITCHER® 0.5-A Step-Down Voltage Regulator: 1 Features 3 Description

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LM2574, LM2574HV
SNVS104D – JUNE 1999 – REVISED APRIL 2016
LM2574x SIMPLE SWITCHER® 0.5-A Step-Down Voltage Regulator

1 Features 3 Description
1• 3.3-V, 5-V, 12-V, 15-V, and Adjustable Output The LM2574xx series of regulators are monolithic
Versions integrated circuits that provide all the active functions
for a step-down (buck) switching regulator, capable of
• Adjustable Version Output Voltage Range: 1.23 V driving a 0.5-A load with excellent line and load
to 37 V (57 V for HV version) ±4% Maximum Over regulation. These devices are available in fixed output
Line and Load Conditions voltages of 3.3 V, 5 V, 12 V, 15 V, and an adjustable
• Specified 0.5-A Output Current output version.
• Wide Input Voltage Range: 40 V, up to 60 V for Requiring a minimum number of external
HV Version components, these regulators are simple to use and
• Requires Only 4 External Components include internal frequency compensation and a fixed-
frequency oscillator.
• 52-kHz Fixed-Frequency Internal Oscillator
• TTL Shutdown Capability, Low-Power Standby The LM2574xx series offers a high-efficiency
Mode replacement for popular three-terminal linear
regulators. Because of its high efficiency, the copper
• High Efficiency traces on the printed-circuit board (PCB) are normally
• Uses Readily Available Standard Inductors the only heat sinking needed.
• Thermal Shutdown and Current-Limit Protection A standard series of inductors optimized for use with
the LM2574 are available from several different
2 Applications manufacturers. This feature greatly simplifies the
• Simple High-Efficiency Step-Down (Buck) design of switch-mode power supplies.
Regulator Other features include a specified ±4% tolerance on
• Efficient Preregulator for Linear Regulators output voltage within specified input voltages and
output load conditions, and ±10% on the oscillator
• On-Card Switching Regulators
frequency. External shutdown is included, featuring
• Positive-to-Negative Converter (Buck-Boost) 50-μA (typical) standby current. The output switch
includes cycle-by-cycle current limiting, as well as
thermal shutdown for full protection under fault
conditions.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
SOIC (14) 8.992 mm × 7.498 mm
LM2574, LM2574HV
PDIP (8) 6.35 mm × 9.81 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application (Fixed Output Voltage Versions)
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM2574, LM2574HV
SNVS104D – JUNE 1999 – REVISED APRIL 2016 www.ti.com
Table of Contents
1 Features .................................................................. 1 7.3 Feature Description................................................. 11
2 Applications ........................................................... 1 7.4 Device Functional Modes........................................ 13
3 Description ............................................................. 1 8 Application and Implementation ........................ 14
4 Revision History..................................................... 2 8.1 Application Information............................................ 14
8.2 Typical Applications ................................................ 19
5 Pin Configuration and Functions ......................... 3
6 Specifications......................................................... 4 9 Power Supply Recommendations...................... 25
6.1 Absolute Maximum Ratings ...................................... 4 10 Layout................................................................... 25
6.2 ESD Ratings.............................................................. 4 10.1 Layout Guidelines ................................................. 25
6.3 Recommended Operating Conditions....................... 4 10.2 Layout Example .................................................... 26
6.4 Thermal Information .................................................. 4 10.3 Grounding ............................................................. 26
6.5 Electrical Characteristics for All Output Voltage 10.4 Thermal Considerations ........................................ 26
Versions ..................................................................... 5 11 Device and Documentation Support ................. 28
6.6 Electrical Characteristics – 3.3-V Version................. 5 11.1 Device Support...................................................... 28
6.7 Electrical Characteristics – 5-V Version.................... 6 11.2 Documentation Support ........................................ 29
6.8 Electrical Characteristics – 12-V Version.................. 6 11.3 Community Resources.......................................... 29
6.9 Electrical Characteristics – 15-V Version.................. 6 11.4 Trademarks ........................................................... 30
6.10 Electrical Characteristics – Adjustable Version....... 7 11.5 Electrostatic Discharge Caution ............................ 30
6.11 Typical Characteristics ............................................ 8 11.6 Glossary ................................................................ 30
7 Detailed Description ............................................ 11 12 Mechanical, Packaging, and Orderable
7.1 Overview ................................................................. 11 Information ........................................................... 30
7.2 Functional Block Diagram ....................................... 11
4 Revision History
Changes from Revision C (April 2013) to Revision D Page
• Added Device Information table, ESD Ratings table, Feature Description section, Device Functional Modes,
Application and Implementation section, Power Supply Recommendations section, Layout section, Device and
Documentation Support section, and Mechanical, Packaging, and Orderable Information section ..................................... 1
• Changed RθJA value in SOIC column to 77.1 ........................................................................................................................ 4
• Split test conditions row of the Electrical Characteristics table to include TJ = 25°C and TJ < 25°C MIN, TYP, and
MAX values............................................................................................................................................................................. 5
• Split test conditions in IL row to rearrange the MIN, TYP, and MAX values ......................................................................... 5
Changes from Revision B (November 2004) to Revision C Page
• Changed layout of National Data Sheet to TI format ............................................................................................................. 1
2 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated
Product Folder Links: LM2574 LM2574HV

LM2574, LM2574HV
www.ti.com SNVS104D – JUNE 1999 – REVISED APRIL 2016
5 Pin Configuration and Functions
P Package
8-Pin PDIP NPA Package
Top View 14-Pin SOIC
Top View
FB 1 8 NC
NC 1 14 NC
SIG_GND 2 7 OUTPUT
NC 2 13 NC
ON/OFF 3 6 NC
FB 3 12 OUTPUT
PWR_GND 4 5 V
IN SIG_GND 4 11 NC
ON/OFF 5 10 V
IN
PWR_GND 6 9 NC
NC 7 8 NC
Pin Functions
PIN
I/O DESCRIPTION
NAME PDIP SOIC
Feedback sense input pin. Connect to the midpoint of feedback divider to set
FB 1 3 I VOUT for ADJ version or connect this pin directly to the output capacitor for a
fixed output version.
1, 2, 7, 8, 9,
NC 8, 6 — No internal connection, but must be soldered to PCB for best heat transfer.
11, 13, 14
Enable input to the voltage regulator. High = OFF and low = ON. Connect to
ON/OFF 3 5 I
GND to enable the voltage regulator. Do not leave this pin float.
Emitter pin of the power transistor. This is a switching node. Attached this pin
OUTPUT 7 12 O
to an inductor and the cathode of the external diode.
Power ground pins. Connect to system ground and SIF GND, ground pins of
PWR_GND 4 6 —
CIN and COUT. Path to CIN must be as short as possible.
Signal ground pin. Ground reference for internal references and logic. Connect
SIG_GND 2 4 —
to system ground.
Supply input pin to collector pin of high-side transistor. Connect to power
VIN 5 10 I supply and input bypass capacitors CIN. Path from VIN pin to high frequency
bypass CIN and PWR GND must be as short as possible.
Copyright © 1999–2016, Texas Instruments Incorporated Submit Documentation Feedback 3

LM2574, LM2574HV
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN MAX UNIT
LM2574 4.5
Maximum supply voltage V
LM2574HV 63
ON/OFF pin input voltage –0.3 VIN V
Output voltage to ground, steady-state –1 V
Power dissipation Internally limited
Lead temperature, soldering (10 s) 260 °C
Maximum junction temperature 150 °C
Storage temperature, Tstg –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings

VALUE UNIT
(1)
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 ±2000 V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)
MIN NOM MAX UNIT
LM2574 40
Supply voltage V
LM2574HV 60
TJ Temperature –40 125 °C
6.4 Thermal Information

LM2574, LM2574HV
(1) (2)
THERMAL METRIC P (PDIP) NPA (SOIC) UNIT
8 PINS 14 PINS
RθJA Junction-to-ambient thermal resistance (3) 60.4 77.1 °C/W
RθJC(top) Junction-to-case (top) thermal resistance (3) 59.9 29.2 °C/W
(3)
RθJB Junction-to-board thermal resistance 37.9 33.3 °C/W
ψJT Junction-to-top characterization parameter 17.1 2 °C/W
ψJB Junction-to-board characterization parameter 37.7 32.8 °C/W
(3)
RθJC(bot) Junction-to-case (bottom) thermal resistance — — °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) The package thermal impedance is calculated in accordance with JESD 51-7.
(3) Thermal resistances were simulated on a 4-layer, JEDEC board.

LM2574, LM2574HV
6.5 Electrical Characteristics for All Output Voltage Versions

TJ = 25°C, and MIN and MAX apply over full operating temperature range. VIN = 12 V for the 3.3-V, 5-V, and adjustable
version, VIN = 25 V for the 12-V version, and VIN = 30 V for the 15-V version, ILOAD = 100 mA (unless otherwise noted).
PARAMETER TEST CONDITIONS MIN (1) TYP MAX (1) UNIT
Adjustable version TJ = 25°C 50 100
Ib Feedback bias current nA
only, VOUT = 5 V –40°C < TJ < 125°C 500
TJ = 25°C 47 52 58
fO Oscillator frequency See (2) kHz
–40°C < TJ < 125°C 42 63
TJ = 25°C 0.9 1.2
VSAT Saturation voltage IOUT = 0.5 A (3) V
–40°C < TJ < 125°C 1.4
DC Maximum duty cycle (ON) See (4) 93% 98%
0.7 1 1.6
ICL Current limit Peak current (3) (2) A
0.65 1.8
Output = 0 V 2
IL Current output leakage mA
Output = –1 V (5) (6) 7.5 30
IQ Quiescent current See (5) 5 10 mA
ISTBY Standby quiescent current ON/OFF pin = 5 V (OFF) 50 200 μA
ON/OFF CONTROL (SEE Figure 27)
TJ = 25°C 2.2 1.4
VIH VOUT = 0 V V
–40°C < TJ < 125°C 2.4
ON/OFF pin logic input level
VOUT = Nominal output TJ = 25°C 1.2 1
VIL V
voltage –40°C < TJ < 125°C 0.8
IH ON/OFF pin = 5 V (OFF) 12 30 μA
ON/OFF pin input current
IIL ON/OFF pin = 0 V (ON) 0 10 μA
(1) All limits specified at room temperature TYP and MAX. All room temperature limits are 100% production tested. All limits at temperature
extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate
Average Outgoing Quality Level.
(2) The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated
output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average power
dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2% (see Figure 6).
(3) Output pin sourcing current. No diode, inductor or capacitor connected to output pin.
(4) Feedback pin removed from output and connected to 0 V.
(5) Feedback pin removed from output and connected to 12 V for the adjustable, 3.3-V, and 5-V versions, and 25 V for the 12-V and 15-V
versions, to force the output transistor OFF.
(6) VIN = 40 V (60 V for high voltage version).
6.6 Electrical Characteristics – 3.3-V Version

TJ = 25°C, and all MIN and MAX apply over full operating temperature range (unless otherwise noted).
PARAMETER (1) TEST CONDITIONS MIN (2) TYP MAX (2) UNIT
VIN = 12 V, ILOAD = 100 mA 3.234 3.3 3.366
LM2574, 4.75 V ≤ VIN ≤ 40 V, TJ = 25°C 3.168 3.3 3.432
VOUT Output voltage 0.1 A ≤ ILOAD ≤ 0.5 A −40°C ≤ TJ ≤ 125°C 3.135 3.465 V
LM2574HV, 4.75 V ≤ VIN ≤ 60 V, TJ = 25°C 3.168 3.3 3.45
0.1 A ≤ ILOAD ≤ 0.5 A −40°C ≤ TJ ≤ 125°C 3.135 3.482
η Efficiency VIN = 12 V, ILOAD = 0.5 A 72%
(1) Test Circuit in Figure 22 and Figure 27.

(2) All limits specified at room temperature and at temperature extremes . All room temperature limits are 100% production tested. All limits
at temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level.

LM2574, LM2574HV
6.7 Electrical Characteristics – 5-V Version

PARAMETER (1) TEST CONDITIONS MIN TYP (2) MAX (2) UNIT
VIN = 12 V, ILOAD = 100 mA 4.9 5 5.1
LM2574, 7 V ≤ VIN ≤ 40 V, TJ = 25°C 4.8 5 5.2
LM2574HV, 7 V ≤ VIN ≤ 60 V, TJ = 25°C 4.8 5 5.225
0.1 A ≤ ILOAD ≤ 0.5 A −40°C ≤ TJ ≤ 125°C 4.75 5.275
(1) Test circuit in Figure 22 and Figure 27.


PARAMETER (1) CONDITIONS MIN TYP (2) MAX (2) UNIT
VIN = 25 V, ILOAD = 100 mA 11.76 12 12.24
LM2574, 15 V ≤ VIN ≤ 40 V, TJ = 25°C 11.52 12 12.48
LM2574HV, 15 V ≤ VIN ≤ 60 V, TJ = 25°C 11.52 12 12.54
0.1 A ≤ ILOAD ≤ 0.5 A −40°C ≤ TJ ≤ 125°C 11.4 12.66


VIN = 30 V, ILOAD = 100 mA 14.7 15 15.3
LM2574, 18 V ≤ VIN ≤ 40 V, TJ = 25°C 14.4 15 15.6
VOUT Output voltage 0.1A ≤ ILOAD ≤ 0.5 A −40°C ≤ TJ ≤ 125°C 14.25 15.75 V
LM2574HV, 18 V ≤ VIN ≤ 60 V, TJ = 25°C 14.4 15 15.68
0.1 A ≤ ILOAD ≤ 0.5 A −40°C ≤ TJ ≤ 125°C 14.25 15.83


LM2574, LM2574HV
6.10 Electrical Characteristics – Adjustable Version

TJ = 25°C, and all MIN and MAX apply over full operating temperature range. VIN = 12 V, ILOAD = 100 mA (unless otherwise
noted).
VIN = 12 V, ILOAD = 100 mA 1.217 1.23 1.243
LM2574, 7 V ≤ VIN ≤ 40 V, TJ = 25°C 1.193 1.23 1.267
0.1 A ≤ ILOAD ≤ 0.5 A,
VFB Feedback voltage VOUT programmed for 5 V −40°C ≤ TJ ≤ 125°C 1.18 1.28 V
LM2574HV, 7 V ≤ VIN ≤ 60 V, TJ = 25°C 1.193 1.23 1.273
0.1 A ≤ ILOAD ≤ 0.5 A,
VOUT programmed for 5 V −40°C ≤ TJ ≤ 125°C 1.18 1.286
η Efficiency VIN = 12 V, VOUT = 5 V, ILOAD = 0.5 A 77%


LM2574, LM2574HV
6.11 Typical Characteristics

See Figure 27.
Figure 1. Normalized Output Voltage Figure 2. Line Regulation
Figure 3. Dropout Voltage Figure 4. Current Limit
Figure 5. Supply Current Figure 6. Standby Quiescent Current

LM2574, LM2574HV
Typical Characteristics (continued)

See Figure 27.
Figure 7. Oscillator Frequency Figure 8. Switch Saturation Voltage
Figure 9. Efficiency Figure 10. Minimum Operating Voltage
Figure 11. Supply Current vs Duty Cycle Figure 12. Feedback Voltage vs Duty Cycle

LM2574, LM2574HV
Typical Characteristics (continued)

See Figure 27.
Figure 13. Feedback Pin Current Figure 14. Junction-to-Ambient Thermal Resistance

LM2574, LM2574HV
7 Detailed Description
7.1 Overview
The LM2574 SIMPLE SWITCHER® regulator is an easy-to-use, non-synchronous, step-down DC-DC converter
with a wide input voltage range from 40 V to up to 60 V for a HV version. It is capable of delivering up to 0.5-A
DC load current with excellent line and load regulation. These devices are available in fixed output voltages of
3.3 V, 5 V, 12 V, 15 V, and an adjustable output version. The family requires few external components and the
pin arrangement was designed for simple, optimum PCB layout.
7.2 Functional Block Diagram
VIN
Unregulated Internal ON / OFF
5 ON / OFF 3
DC Input Regulator
+ 1
CIN Feedback Fixed Gain
R2
Error Amp
+ Compatator 0.5 Amp
+ Switch
R1 ±
± DRIVER
Output L1 VOUT
7 +
Signal 2 D1
1.23 V COUT L
GND 52 kHz
BAND ± GAP Thermal Current O
OSCILLATOR Reset 4
REFRENCE Shutdown Limit A
D
Pwr Gnd
Copyright © 2016, Texas Instruments Incorporated

Note: Pin numbers are for the 8-pin PDIP package
R1 = 1 k
3.3 V, R2 = 1.7 k
5 V, R2 = 3.1 k
12 V, R2 = 8.84 k
15 V, R2 = 11.3 k
For adjustable version,
R1 = Open, R2 = 0 Ω
7.3 Feature Description

7.3.1 Current Limit
The LM2574 device has current limiting to prevent the switch current from exceeding safe values during an
accidental overload on the output. This value (ICL) can be found in Electrical Characteristics for All Output
Voltage Versions.
7.3.2 Undervoltage Lockout

In some applications, it is desirable to keep the regulator off until the input voltage reaches a certain threshold.
An undervoltage lockout circuit which accomplishes this task is shown in Figure 15 while Figure 16 shows the
same circuit applied to a buck-boost configuration. These circuits keep the regulator off until the input voltage
reaches a predetermined level in Equation 1.
VTH ≈ VZ1 + 2 VBE (1)

LM2574, LM2574HV
Feature Description (continued)
Note: Complete circuit not shown (see Figure 20).

Note: Pin numbers are for 8-pin PDIP package.
Figure 15. Undervoltage Lockout for Buck Circuit
Note: Complete circuit not shown (see Figure 20).

Figure 16. Undervoltage Lockout for Buck-Boost Circuit
7.3.3 Delayed Start-Up

The ON/OFF pin can be used to provide a delayed start-up feature as shown in Figure 17. With an input voltage
of 20 V and for the part values shown, the circuit provides approximately 10 ms of delay time before the circuit
begins switching. Increasing the RC time constant can provide longer delay times. But excessively large RC time
constants can cause problems with input voltages that are high in 60-Hz or 120-Hz ripple, by coupling the ripple
into the ON/OFF pin.
7.3.4 Adjustable Output, Low-Ripple Power Supply

A 500-mA power supply that features an adjustable output voltage is shown in Figure 18. An additional L-C filter
that reduces the output ripple by a factor of 10 or more is included in this circuit.

LM2574, LM2574HV
Feature Description (continued)
Note: Complete circuit not shown.

Figure 17. Delayed Start-Up
Figure 18. 1.2-V to 55-V Adjustable 500-mA Power Supply With Low-Output Ripple
7.4 Device Functional Modes

7.4.1 Shutdown Mode
The ON/OFF pin provides electrical ON and OFF control for the LM2574. When the voltage of this pin is higher
than 1.4 V, the device is shutdown mode. The typical standby current in this mode is 50 μA.
7.4.2 Active Mode

When the voltage of the ON/OFF pin is below 1.2 V, the device starts switching and the output voltage rises until
it reaches a normal regulation voltage.

LM2574, LM2574HV
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information

8.1.1 Input Capacitor (CIN)
To maintain stability, the regulator input pin must be bypassed with at least a 22-μF electrolytic capacitor. The
leads of the capacitor must be kept short, and located near the regulator.
If the operating temperature range includes temperatures below −25°C, the input capacitor value may need to be
larger. With most electrolytic capacitors, the capacitance value decreases and the ESR increases with lower
temperatures and age. Paralleling a ceramic or solid tantalum capacitor increases the regulator stability at cold
temperatures. For maximum capacitor operating lifetime, the RMS ripple current rating of the capacitor must be
greater than Equation 2.
t
1.2 ´ ON ´ ILOAD
T
where
t ON VOUT
=
• T VIN for a buck regulator
t ON VOUT
=
• T VOUT + VIN for a buck-boost regulator (2)
8.1.2 Inductor Selection

All switching regulators have two basic modes of operation: continuous and discontinuous. The difference
between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a
period of time in the normal switching cycle. Each mode has distinctively different operating characteristics,
which can affect the regulator performance and requirements.
The LM2574 (or any of the SIMPLE SWITCHER family) can be used for both continuous and discontinuous
modes of operation.
In many cases the preferred mode of operation is in the continuous mode. It offers better load regulation, lower
peak switch, inductor, and diode currents, and can have lower output ripple voltage. But it does require relatively
large inductor values to keep the inductor current flowing continuously, especially at low output load currents.
To simplify the inductor selection process, an inductor selection guide (nomograph) was designed. This guide
assumes continuous mode operation, and selects an inductor that allows a peak-to-peak inductor ripple current
(ΔIIND) to be a certain percentage of the maximum design load current. In the LM2574 SIMPLE SWITCHER, the
peak-to-peak inductor ripple current percentage (of load current) is allowed to change as different design load
currents are selected. By allowing the percentage of inductor ripple current to increase for lower current
applications, the inductor size and value can be kept relatively low.
8.1.3 Inductor Ripple Current

When the switcher is operating in the continuous mode, the inductor current waveform ranges from a triangular
to a sawtooth type of waveform (depending on the input voltage). For a given input voltage and output voltage,
the peak-to-peak amplitude of this inductor current waveform remains constant. As the load current rises or falls,
the entire sawtooth current waveform also rises or falls. The average DC value of this waveform is equal to the
DC load current (in the buck regulator configuration).

LM2574, LM2574HV
Application Information (continued)

If the load current drops to a low enough level, the bottom of the sawtooth current waveform reaches zero, and
the switcher changes to a discontinuous mode of operation. This is a perfectly acceptable mode of operation.
Any buck switching regulator (no matter how large the inductor value is) is forced to run discontinuous if the load
current is light enough.
The curve shown in Figure 19 illustrates how the peak-to-peak inductor ripple current (ΔIIND) is allowed to change
as different maximum load currents are selected, and also how it changes as the operating point varies from the
upper border to the lower border within an inductance region (see Inductor Selection).
Figure 19. Inductor Ripple Current (ΔiIND) Range
Consider the following example:

VOUT = 5 V at 0.4 A
VIN = 10-V minimum up to 20-V maximum
The selection guide in Figure 24 shows that for a 0.4-A load current, and an input voltage range between 10 V
and 20 V, the inductance region selected by the guide is 330 μH. This value of inductance allows a peak-to-peak
inductor ripple current (ΔIIND) to flow that is a percentage of the maximum load current. For this inductor value,
the ΔIIND also varies depending on the input voltage. As the input voltage increases to 20 V, it approaches the
upper border of the inductance region, and the inductor ripple current increases. Referring to the curve in
Figure 19, it can be seen that at the 0.4-A load current level, and operating near the upper border of the 330-μH
inductance region, the ΔIIND is 53% of 0.4 A, or 212 mAp-p.
This ΔIIND is important because from this number the peak inductor current rating can be determined, the
minimum load current required before the circuit goes to discontinuous operation, and also, knowing the ESR of
the output capacitor, the output ripple voltage can be calculated, or conversely, measuring the output ripple
voltage and knowing the ΔIIND, the ESR can be calculated.
From the previous example, the peak-to-peak inductor ripple current (ΔIIND) = 212 mAp-p. When the ΔIND value is
known, the following three formulas can be used to calculate additional information about the switching regulator
circuit:
1. Peak inductor or peak switch current in Equation 3.
æ DI ö æ 212 ö
= ç ILOAD + IND ÷ = ç 0.4 A + = 506 mA
è 2 ø è 2 ÷ø (3)
2. Minimum load current before the circuit becomes discontinuous in Equation 4.
DI 212
= IND = = 106 mA
2 2 (4)
3. Output ripple voltage = (ΔIIND) × (ESR of COUT)

LM2574, LM2574HV
Application Information (continued)

The selection guide chooses inductor values suitable for continuous mode operation, but if the inductor value
chosen is prohibitively high, the designer should investigate the possibility of discontinuous operation.
Inductors are available in different styles such as pot core, toroid, E-frame, bobbin core, and so forth, as well as
different core materials, such as ferrites and powdered iron. The least expensive, the bobbin core type, consists
of wire wrapped on a ferrite rod core. This type of construction makes for an inexpensive inductor, but because
the magnetic flux is not completely contained within the core, it generates more electro-magnetic interference
(EMI). This EMl can cause problems in sensitive circuits, or can give incorrect scope readings because of
induced voltages in the scope probe.
The inductors listed in the selection chart include powdered iron toroid for Pulse Engineering, and ferrite bobbin
core for Renco.
An inductor must not be operated beyond its maximum rated current because it may saturate. When an inductor
begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC
resistance of the winding). This can cause the inductor current to rise very rapidly and affects the energy storage
capabilities of the inductor and could cause inductor overheating. Different inductor types have different
saturation characteristics, and consider this when selecting an inductor. The inductor manufacturers' data sheets
include current and energy limits to avoid inductor saturation.
8.1.4 Output Capacitor

An output capacitor is required to filter the output voltage and is needed for loop stability. The capacitor must be
located near the LM2574 using short PCB traces. Standard aluminum electrolytics are usually adequate, but low
ESR types are recommended for low output ripple voltage and good stability. The ESR of a capacitor depends
on many factors, some which are: the value, the voltage rating, physical size, and the type of construction. In
general, low-value or low-voltage (less than 12 V) electrolytic capacitors usually have higher ESR numbers.
The amount of output ripple voltage is primarily a function of the ESR (Equivalent Series Resistance) of the
output capacitor and the amplitude of the inductor ripple current, ΔIIND (see Inductor Ripple Current (ΔiIND)).
The lower capacitor values (100 μF to 330 μF) allows typically 50 mV to 150 mV of output ripple voltage, while
larger-value capacitors reduce the ripple to approximately 20 mV to 50 mV (as seen in Equation 5).
Output Ripple Voltage = (ΔIIND) (ESR of COUT) (5)
To further reduce the output ripple voltage, several standard electrolytic capacitors may be paralleled, or a
higher-grade capacitor may be used. Such capacitors are often called high-frequency, low-inductance, or low-
ESR. These reduce the output ripple to 10 mV or 20 mV. However, when operating in the continuous mode,
reducing the ESR below 0.03 Ω can cause instability in the regulator.
Tantalum capacitors can have a very low ESR, and must be carefully evaluated if it is the only output capacitor.
Because of their good low temperature characteristics, a tantalum can be used in parallel with aluminum
electrolytics, with the tantalum making up 10% or 20% of the total capacitance.
The ripple current rating of the capacitor at 52 kHz must be at least 50% higher than the peak-to-peak inductor
ripple current.
8.1.5 Catch Diode

Buck regulators require a diode to provide a return path for the inductor current when the switch is off. This diode
must be located close to the LM2574 using short leads and short printed-circuit traces.
Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best efficiency,
especially in low output voltage switching regulators (less than 5 V). fast-recovery, high-efficiency, or ultra-fast
recovery diodes are also suitable, but some types with an abrupt turnoff characteristic may cause instability and
EMI problems. A fast-recovery diode with soft recovery characteristics is a better choice. Standard 60-Hz diodes
(for example, 1N4001 or 1N5400, and so forth) are also not suitable. See Table 1 for Schottky and soft fast-
recovery diode selection guide.

LM2574, LM2574HV
Table 1. Diode Selection Guide

1-A DIODES
VR
SCHOTTKY FAST RECOVERY
1N5817
20 V SR102
MBR120P
1N5818
SR103 The following diodes are all rated to 100 V
30 V 11DQ03
MBR130P
10JQ030
1N5819
SR104 11DF1
40 V 11DQ04 10JF1
11JQ04 MUR110
MBR140P HER102
MBR150
SR105
50 V
11DQ05
11JQ05
MBR160
SR106
60 V
11DQ06
11JQ06
90 V 11DQ09
8.1.6 Output Voltage Ripple and Transients

The output voltage of a switching power supply contains a sawtooth ripple voltage at the switcher frequency,
typically about 1% of the output voltage, and may also contain short voltage spikes at the peaks of the sawtooth
waveform.
The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output
capacitor (see Inductor Selection).
The voltage spikes are present because of the fast switching action of the output switch, and the parasitic
inductance of the output filter capacitor. To minimize these voltage spikes, special low inductance capacitors can
be used, and their lead lengths must be kept short. Wiring inductance, stray capacitance, as well as the scope
probe used to evaluate these transients, all contribute to the amplitude of these spikes.
An additional small LC filter (20 μH and 100 μF) can be added to the output (as shown in Figure 18) to further
reduce the amount of output ripple and transients. A 10 × reduction in output ripple voltage and transients is
possible with this filter.
8.1.7 Feedback Connection

The LM2574 (fixed voltage versions) feedback pin must be wired to the output voltage point of the switching
power supply. When using the adjustable version, physically locate both output voltage programming resistors
near the LM2574 to avoid picking up unwanted noise. Avoid using resistors greater than 100 kΩ because of the
increased chance of noise pickup.
8.1.8 ON/OFF Input

For normal operation, the ON/OFF pin must be grounded or driven with a low-level TTL voltage (typically less
than 1.6 V). To put the regulator into standby mode, drive this pin with a high-level TTL or CMOS signal. The
ON/OFF pin can be safely pulled up to +VIN without a resistor in series with it. The ON/OFF pin must not be left
open.

LM2574, LM2574HV
8.1.9 Additional Applications
8.1.9.1 Inverting Regulator

Figure 20 shows a LM2574-12 in a buck-boost configuration to generate a negative 12-V output from a positive
input voltage. This circuit bootstraps the ground pin of the regulator to the negative output voltage, then by
grounding the feedback pin, the regulator senses the inverted output voltage and regulates it to −12 V.
Note: Pin numbers are for the 8-pin PDIP package.
Figure 20. Inverting Buck-Boost Develops, 12 V
For an input voltage of 8 V or more, the maximum available output current in this configuration is approximately
100 mA. At lighter loads, the minimum input voltage required drops to approximately 4.7 V.
The switch currents in this buck-boost configuration are higher than in the standard buck-mode design, thus
lowering the available output current. Also, the start-up input current of the buck-boost converter is higher than
the standard buck-mode regulator, and this may overload an input power source with a current limit less than
0.6 A. Using a delayed turnon or an undervoltage lockout circuit (described in Negative Boost Regulator) would
allow the input voltage to rise to a high enough level before the switcher would be allowed to turn on.
Because of the structural differences between the buck and the buck-boost regulator topologies, the design
procedure can not be used to select the inductor or the output capacitor. The recommended range of inductor
values for the buck-boost design is between 68 μH and 220 μH, and the output capacitor values must be larger
than what is normally required for buck designs. Low-input voltages or high-output currents require a large value
output capacitor (in the thousands of micro Farads).
The peak inductor current, which is the same as the peak switch current, can be calculated from Equation 6.
ILOAD ´ (VIN + VOUT ) + VIN ´ VOUT 1
IP » ´
VIN VIN + VOUT 2 ´ L 1 ´ f OSC
where
• fosc = 52 kHz. Under normal continuous inductor current operating conditions,
• the minimum VIN represents the worst case. Select an inductor that is rated for the peak current anticipated.
(6)
Also, the maximum voltage appearing across the regulator is the absolute sum of the input and output voltage.
For a −12-V output, the maximum input voltage for the LM2574 is 28 V, or 48 V for the LM2574HV.
8.1.9.2 Negative Boost Regulator

Another variation on the buck-boost topology is the negative boost configuration. The circuit in Figure 21 accepts
an input voltage ranging from −5 V to −12 V and provides a regulated −12-V output. Input voltages greater than
−12 V causes the output to rise greater than −12 V, but does not damage the regulator.

LM2574, LM2574HV
Figure 21. Negative Boost
Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low
input voltages. Output load current limitations are a result of the maximum current rating of the switch. Also,
boost regulators can not provide current-limiting load protection in the event of a shorted load, so some other
means (such as a fuse) may be necessary.
8.2 Typical Applications

8.2.1 Fixed Output Voltage Applications
CIN: 22 μF, 75 V
Aluminum electrolytic
COUT: 220 μF, 25 V
Aluminum electrolytic
D1: Schottky, 11DQ06
L1: 330 μH, 52627
(for 5 V in, 3.3 V out, use
100 μH, RL-1284-100)
R1: 2k, 0.1%
R2: 6.12k, 0.1%
Figure 22. Fixed Output Voltage Versions

LM2574, LM2574HV
Typical Applications (continued)

8.2.1.1 Design Requirements
The design requirements for the fixed output voltage application is provided in Table 2.
Table 2. Design Parameters

PARAMETER EXAMPLE VALUE
Regulated output voltage (3.3 V, 5 V, 12 V, or 15 V), VOUT 5V
Maximum input voltage, VIN(Max) 15 V
Maximum load current, ILOAD(Max) 0.4 A
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Inductor Selection (L1)

Select the correct Inductor value selection guide from Figure 23, Figure 24, Figure 25, or Figure 26 (output
voltages of 3.3 V, 5 V, 12 V, or 15 V respectively).
From the inductor value selection guide, identify the inductance region intersected by VIN(Max) and ILOAD(Max).
The inductance area intersected by the 15-V line and 0.4-A line is 330.
Select an appropriate inductor from Table 3. Part numbers are listed for three inductor manufacturers. The
inductor chosen must be rated for operation at the LM2574 switching frequency (52 kHz) and for a current rating
of 1.5 × ILOAD. For additional inductor information, see Inductor Selection. The required inductor value is 330 μH.
From Table 3, choose Pulse Engineering PE-52627, Renco RL-1284-330, or NPI NP5920/5921.
Table 3. Inductor Selection By Manufacturer's Part Number

INDUCTOR VALUE PULSE ENG. RENCO NPI
68 μH * RL-1284-68-43 NP5915
100 μH * RL-1284-100-43 NP5916
150 μH 52625 RL-1284-150-43 NP5917
220 μH 52626 RL-1284-220-43 NP5918/5919
330 μH 52627 RL-1284-330-43 NP5920/5921
470 μH 52628 RL-1284-470-43 NP5922
680 μH 52629 RL-1283-680-43 NP5923
1000 μH 52631 RL-1283-1000-43 *
1500 μH * RL-1283-1500-43 *
2200 μH * RL-1283-2200-43 *
8.2.1.2.2 Output Capacitor Selection (COUT)

The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation and an acceptable output ripple voltage, (approximately 1% of the output
voltage) a value between 100 μF and 470 μF is recommended. COUT = 100-μF to 470-μF standard aluminum
electrolytic.
The voltage rating of the capacitor must be at least 1.5 times greater than the output voltage. For a 5-V regulator,
a rating of at least 8 V is appropriate, and a 10-V or 15-V rating is recommended. Capacitor voltage rating =
20 V.
Higher voltage electrolytic capacitors generally have lower ESR numbers, and for this reason it may be
necessary to select a capacitor rated for a higher voltage than would normally be needed.

LM2574, LM2574HV
8.2.1.2.3 Catch Diode Selection (D1)

The catch-diode current rating must be at least 1.5 times greater than the maximum load current. Also, if the
power supply design must withstand a continuous output short, the diode must have a current rating equal to the
maximum current limit of the LM2574. The most stressful condition for this diode is an overload or shorted output
condition. For this example, a 1-A current rating is adequate.
The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Use a 20-V
1N5817 or SR102 Schottky diode, or any of the suggested fast-recovery diodes shown in Table 1.
8.2.1.2.4 Input Capacitor (CIN)

An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable
operation. A 22-μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient
bypassing.
8.2.1.3 Application Curves
Figure 23. 3.3-V LM2574HV Inductor Selection Guide Figure 24. 5-V LM2574HV Inductor Selection Guide
Figure 25. 12-V LM2574HV Inductor Selection Guide Figure 26. 15-V LM2574HV Inductor Selection Guide

LM2574, LM2574HV
8.2.2 Adjustable Output Voltage Applications
Figure 27. Adjustable Output Voltage Version
8.2.2.1 Design Requirements

The design requirements for the fixed output voltage application is provided in Table 4.
Table 4. Design Parameters

PARAMETER EXAMPLE VALUE
Regulated output voltage, VOUT 24 V
Maximum input voltage, VIN(Max) 40 V
Maximum load current, ILOAD(Max) 0.4 A
Switching frequency, F 52 kHz
8.2.2.2 Detailed Design Procedure
8.2.2.2.1 Programming Output Voltage

Selecting R1 and R2, as shown in Figure 27.
Use Equation 7 to select the appropriate resistor values.
æ R ö
VOUT = VREF ´ ç 1 + 2 ÷
è R1 ø
where
• VREF = 1.23 V (7)
R1 can be between 1k and 5k as in Equation 8. For best temperature coefficient and stability with time, use 1%
metal film resistors.
æV ö
R 2 = R 1 ´ ç OUT - 1÷
è VREF ø (8)
For this example, use Equation 9 and Equation 10.
æ R ö
VOUT = 1.23 ´ ç 1 + 2 ÷
è R1 ø
select
• R1 = 1k (9)
æV ö æ 24 V ö
R 2 = R 1 ´ ç OUT - 1÷ = 1k ´ ç - 1÷
V
è REF ø è 1.23 V ø (10)
R2 = 1k (19.51−1) = 18.51k, closest 1% value is 18.7k

LM2574, LM2574HV
8.2.2.2.2 Inductor Selection (L1)

Calculate the inductor Volt × microsecond constant, E × T (V × μs), from Equation 11.
V 1000
E ´ T = (VIN - VOUT )´ OUT ´ (V ´ µs )
VIN F (kHz ) (11)
For this example, calculate E × T (V × μs) using Equation 12.
24 1000
E ´ T = (40 - 24 )´ ´ = 185 V ´ µs
40 52 (12)
Use the E × T value from the previous formula and match it with the E × T number on the vertical axis of the
inductor value selection guide shown in Figure 32. For this example, E × T = 185 V × μs.
On the horizontal axis, select the maximum load current, ILOAD(Max) = 0.4 A.
Identify the inductance region intersected by the E × T value and the maximum load current value, and note the
inductor value for that region, inductance region = 1000.
Select an appropriate inductor from the table shown in Table 3. Part numbers are listed for three inductor
manufacturers. The inductor chosen must be rated for operation at the LM2574 switching frequency (52 kHz) and
for a current rating of 1.5 × ILOAD. For additional inductor information, see Inductor Selection.
8.2.2.2.3 Output Capacitor Selection (COUT)

The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation, the capacitor must satisfy the requirement in Equation 13.
VIN(MAX )
C OUT ³ 13300 ´ (µF )
VOUT ´ L (µH) (13)
Equation 13 yields capacitor values between 5 μF and 1000 μF that satisfies the loop requirements for stable
operation. But to achieve an acceptable output ripple voltage, (approximately 1% of the output voltage) and
transient response, the output capacitor may need to be several times larger than the above formula yields.
The voltage rating of the capacitor must be at last 1.5 times greater than the output voltage. For a 24-V regulator,
a rating of at least 35 V is recommended. Higher voltage electrolytic capacitors generally have lower ESR
numbers, and for this reasion it may be necessary to select a capacitor rate for a higher voltage than would
normally be needed.
40
C OUT > 13300 ´ = 22.2 µF
24 ´ 1000 (14)
However, for acceptable output ripple voltage select:
COUT ≥ 100 μF
COUT = 100 μF electrolytic capacitor
8.2.2.2.4 Catch Diode Selection (D1)

The catch-diode current rating must be at least 1.5 times greater than the maximum load current. Also, if the
power supply design must withstand a continuous output short, the diode must have a current rating equal to the
maximum current limit of the LM2574. The most stressful condition for this diode is an overload or shorted output
condition. Suitable diodes are shown in Table 1. For this example, a 1-A current rating is adequate.
The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Use a 50-V
MBR150 or 11DQ05 Schottky diode, or any of the suggested fast-recovery diodes in Table 1.
8.2.2.2.5 Input Capacitor (CIN)

An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable
operation. A 22-μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient
bypassing (see Table 1).

LM2574, LM2574HV
8.2.2.3 Application Curves
Output pin voltage, 10 V/div, Horizontal time base, Output pin voltage, 10 V/div, Horizontal time base,
Inductor current, 0.2 A/div, 5 μs/div, Inductor current, 0.2 A/div, 5 μs/div,
Output ripple voltage, VOUT = 5 V, Output ripple voltage, VOUT = 5 V,
20 mV/div, 500-mA load current, 20 mV/div, 100-mA load current,
AC-coupled L = 330 Μh AC-coupled L = 100 Μh
Figure 28. Continuous Mode Switching Waveforms Figure 29. Discontinuous Mode Switching Waveforms
Output voltage, 50 V/div, 500 mA load, Output voltage, 50 V/div, 250 mA load,
AC-coupled, L = 330 Μh, AC-coupled, L = 68 Μh,
100-mA to 500-mA load pulse, COUT = 300 Μf, 50-mA to 250-mA load pulse, COUT = 470 Μf,
Horizontal time base: 200 μs/div Horizontal time base: 200 μs/div
Figure 30. Transient Response for Figure 31. Transient Response for
Continuous Mode Operation Discontinuous Mode Operation
Figure 32. Adjustable LM2574HV Inductor Selection Guide

LM2574, LM2574HV
9 Power Supply Recommendations

As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring
inductance generate voltage transients which can cause problems. For minimal inductance and ground loops, the
length of the leads indicated by heavy lines must be kept as short as possible. Single-point grounding (as
indicated) or ground plane construction must be used for best results. When using the adjustable version,
physically locate the programming resistors near the regulator, to keep the sensitive feedback wiring short.
10 Layout
10.1 Layout Guidelines

The layout is critical for the proper operation of switching power supplies. First, the ground plane area must be
sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce the effects
of switching noise. Switch mode converters are very fast switching devices. In such cases, the rapid increase of
input current combined with the parasitic trace inductance generates unwanted L di/dt noise spikes. The
magnitude of this noise tends to increase as the output current increases. This noise may turn into
electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, take care in
the layout to minimize the effect of this switching noise.
The most important layout rule is to keep the AC current loops as small as possible. Figure 33 shows the current
flow in a buck converter. The top schematic shows a dotted line which represents the current flow during the top
switch ON-state. The middle schematic shows the current flow during the top switch OFF-state. The bottom
schematic shows the currents referred to as AC currents. These AC currents are the most critical because they
are changing in a very short time period. The dotted lines of the bottom schematic are the traces to keep as short
and wide as possible. This also yields a small loop area reducing the loop inductance. To avoid functional
problems due to layout, review the PCB layout example. Best results are achieved if the placement of the
LM2574 device, the bypass capacitor, the Schottky diode, RFBB, RFBT, and the inductor are placed as shown in
the example. In the layout shown, R1 = RFBB and R2 = RFBT. TI also recommends using 2-oz. copper boards
or heavier to help thermal dissipation and to reduce the parasitic inductances of board traces. See the application
note AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for more information.
Figure 33. Buck Converter Current Flow

LM2574, LM2574HV
10.2 Layout Example
Figure 34. LM2574 Adjustable Output Voltage Layout
10.3 Grounding
The 8-pin molded PDIP and the 14-pin SOIC package have separate power and signal ground pins. Both ground
pins must be soldered directly to wide printed-circuit board copper traces to assure low inductance connections
and good thermal properties.
10.4 Thermal Considerations

The 8-pin PDIP (P) package and the 14-pin SOIC (NPA) package are molded plastic packages with solid copper
lead frames. The copper lead frame conducts the majority of the heat from the die, through the leads, to the
printed-circuit board copper, which acts as the heat sink. For best thermal performance, wide copper traces must
be used, and all ground and unused pins must be soldered to generous amounts of printed-circuit board copper,
such as a ground plane. Large areas of copper provide the best transfer of heat (lower thermal resistance) to the
surrounding air, and even double-sided or multilayer boards provide better heat paths to the surrounding air.
Unless the power levels are small, using a socket for the 8-pin package is not recommended because of the
additional thermal resistance it introduces, and the resultant higher junction temperature.
Because of the 0.5-A current rating of the LM2574, the total package power dissipation for this switcher is quite
low, ranging from approximately 0.1 W up to 0.75 W under varying conditions. In a carefully engineered printed-
circuit board, both the P and the NPA package can easily dissipate up to 0.75 W, even at ambient temperatures
of 60°C, and still keep the maximum junction temperature less than 125°C.
A curve, Figure 14, displaying thermal resistance versus PCB area for the two packages is shown in Typical
Characteristics.
These thermal resistance numbers are approximate, and there can be many factors that affect the final thermal
resistance. Some of these factors include board size, shape, thickness, position, location, and board
temperature. Other factors are, the area of printed-circuit copper, copper thickness, trace width, multi-layer,
single- or double-sided, and the amount of solder on the board. The effectiveness of the PCB to dissipate heat
also depends on the size, number and spacing of other components on the board. Furthermore, some of these
components, such as the catch diode and inductor generate some additional heat. Also, the thermal resistance
decreases as the power level increases because of the increased air current activity at the higher power levels,
and the lower surface to air resistance coefficient at higher temperatures.
The data sheet thermal resistance curves can estimate the maximum junction temperature based on operating
conditions. ln addition, the junction temperature can be estimated in actual circuit operation by using
Equation 15.
Tj = Tcu + (θj-cu × PD) (15)

LM2574, LM2574HV
Thermal Considerations (continued)

With the switcher operating under worst case conditions and all other components on the board in the intended
enclosure, measure the copper temperature (Tcu ) near the IC. This can be done by temporarily soldering a small
thermocouple to the PCB copper near the IC, or by holding a small thermocouple on the PCB copper using
thermal grease for good thermal conduction.
The thermal resistance (θj-cu) for the two packages is:
θj-cu = 42°C/W for the P-8 package
θj-cu = 52°C/W for the NPA-14 package
The power dissipation (PD) for the IC could be measured, or it can be estimated by using Equation 16.
V
PD = VIN ´ IS + OUT ´ ILOAD ´ VSAT
VIN
where
• IS is obtained from the typical supply current curve (adjustable version use the supply current vs duty cycle
curve) (16)

LM2574, LM2574HV
11 Device and Documentation Support
11.1 Device Support

11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.1.2 Device Nomenclature
11.1.2.1 Buck Regulator

A switching regulator topology in which a higher voltage is converted to a lower voltage. Also known as a step-
down switching regulator.
11.1.2.2 Buck-Boost Regulator

A switching regulator topology in which a positive voltage is converted to a negative voltage without a
transformer.
11.1.2.3 Duty Cycle (D)

The ratio of the ON-time of the output switch to the oscillator period calculated with Equation 17 for buck
regulators and Equation 18 for buck-boost regulators.
t V
D = ON = OUT
T VIN (17)
t ON VOUT
D= =
T VOUT + VIN (18)
11.1.2.4 Catch Diode or Current Steering Diode

This diode provides a return path for the load current when the LM2574 switch is OFF.
In terms of efficiency (η), the proportion of input power actually delivered to the load calculated with Equation 19.
P POUT
h = OUT =
PIN POUT + PLOSS (19)
11.1.2.5 Capacitor Equivalent Series Resistance (ESR)

The purely resistive component of a real capacitor's impedance (see Figure 35) can causes power loss resulting
in capacitor heating, which directly affects the operating lifetime of the capacitor. When used as a switching
regulator output filter, higher ESR values result in higher output ripple voltages.
Figure 35. Simple Model Of A Real Capacitor
Most standard aluminum electrolytic capacitors in the 100 μF to 1000 μF range have 0.5-Ω to 0.1-Ω ESR.
Higher-grade capacitors (low-ESR, high-frequency, or low-inductance) in the 100 μF to 1000 μF range generally
have ESR of less than 0.15 Ω.
11.1.2.6 Equivalent Series Inductance (ESL)

The pure inductance component of a capacitor is seen in Figure 35. The amount of inductance is determined to a
large extent on the capacitor's construction. In a buck regulator, this unwanted inductance causes voltage spikes
to appear on the output.

LM2574, LM2574HV
Device Support (continued)

11.1.2.7 Output Ripple Voltage
The AC component of the output voltage of the switching regulator is usually dominated by the output capacitor's
ESR multiplied by the inductor's ripple current (ΔIIND). The peak-to-peak value of this sawtooth ripple current can
be determined by reading Inductor Ripple Current (ΔiIND).
11.1.2.8 Capacitor Ripple Current

The RMS value of the maximum allowable alternating current at which a capacitor can be operated continuously
at a specified temperature.
11.1.2.9 Standby Quiescent Current (ISTBY)

Supply current required by the LM2574 when in the standby mode (ON/OFF pin is driven to TTL-high voltage,
thus turning the output switch OFF).
11.1.2.10 Inductor Ripple Current (ΔiIND)

The peak-to-peak value of the inductor current waveform, typically a sawtooth waveform when the regulator is
operating in the continuous mode (vs. discontinuous mode).
11.1.2.11 Continuous and Discontinuous Mode Operation

These mode operations relate to the inductor current. In the continuous mode, the inductor current is always
flowing and never drops to zero, versus the discontinuous mode, where the inductor current drops to zero for a
period of time in the normal switching cycle.
11.1.2.12 Inductor Saturation

The condition which exists when an inductor cannot hold any more magnetic flux. When an inductor saturates,
the inductor appears less inductive and the resistive component dominates. Inductor current is then limited only
by the DC resistance of the wire and the available source current.
11.1.2.13 Operating Volt Microsecond Constant (E × Top)

The product (in VoIt × μs) of the voltage applied to the inductor and the time the voltage is applied. This E × Top
constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core,
the core area, the number of turns, and the duty cycle.
11.2 Documentation Support

11.2.1 Related Documentation
For related documentation see the following:
AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines, SNVA054
11.3 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.

LM2574, LM2574HV
11.4 Trademarks
E2E is a trademark of Texas Instruments.
SIMPLE SWITCHER is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

PACKAGE OPTION ADDENDUM
www.ti.com 2-Sep-2017
PACKAGING INFORMATION
Orderable Device Status Package Type Package Pins Package Eco Plan Lead/Ball Finish MSL Peak Temp Op Temp (°C) Device Marking Samples
(1) Drawing Qty (2) (6) (3) (4/5)
LM2574HVM-12/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -12 P+
LM2574HVM-15 NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574HVM
-15 P+
LM2574HVM-15/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -15 P+
LM2574HVM-3.3/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -3.3 P+
LM2574HVM-5.0 NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574HVM
-5.0 P+
LM2574HVM-5.0/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -5.0 P+
LM2574HVM-ADJ NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574HVM
-ADJ P+
LM2574HVM-ADJ/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -ADJ P+
LM2574HVMX-12/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -12 P+
LM2574HVMX-15/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -15 P+
LM2574HVMX-3.3/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-4-260C-72 HR -40 to 125 LM2574HVM
& no Sb/Br) -3.3 P+
LM2574HVMX-5.0 NRND SOIC NPA 14 1000 TBD Call TI Call TI -40 to 125 LM2574HVM
-5.0 P+
LM2574HVMX-5.0/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -5.0 P+
LM2574HVMX-ADJ/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM
& no Sb/Br) -ADJ P+
LM2574HVN-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN
& no Sb/Br) -12 P+
LM2574HVN-15/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN
& no Sb/Br) -15 P+
LM2574HVN-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN
& no Sb/Br) -5.0 P+
Addendum-Page 1
Orderable Device Status Package Type Package Pins Package Eco Plan Lead/Ball Finish MSL Peak Temp Op Temp (°C) Device Marking Samples
(1) Drawing Qty (2) (6) (3) (4/5)
LM2574HVN-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN

& no Sb/Br) -ADJ P+
LM2574M-12/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -12 P+
LM2574M-3.3/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -3.3 P+
LM2574M-5.0 NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574M
-5.0 P+
LM2574M-5.0/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -5.0 P+
LM2574M-ADJ NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574M
-ADJ P+
LM2574M-ADJ/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -ADJ P+
LM2574MX-12/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -12 P+
LM2574MX-3.3/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-4-260C-72 HR -40 to 125 LM2574M
& no Sb/Br) -3.3 P+
LM2574MX-5.0 NRND SOIC NPA 14 1000 TBD Call TI Call TI -40 to 125 LM2574M
-5.0 P+
LM2574MX-5.0/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -5.0 P+
LM2574MX-ADJ/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS CU SN Level-3-260C-168 HR -40 to 125 LM2574M
& no Sb/Br) -ADJ P+
LM2574N-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574N
& no Sb/Br) -12 P+
LM2574N-3.3/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574N
& no Sb/Br) -3.3 P+
LM2574N-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574N
& no Sb/Br) -5.0 P+
LM2574N-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS CU SN Level-1-NA-UNLIM -40 to 125 LM2574N
& no Sb/Br) -ADJ P+
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
Addendum-Page 2
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 3
PACKAGE MATERIALS INFORMATION
www.ti.com 24-Aug-2017
TAPE AND REEL INFORMATION
*All dimensions are nominal

Device Package Package Pins SPQ Reel Reel A0 B0 K0 P1 W Pin1
Type Drawing Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LM2574HVMX-12/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574HVMX-15/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574HVMX-3.3/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574HVMX-5.0 SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574HVMX-5.0/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574HVMX-ADJ/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574MX-12/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574MX-3.3/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574MX-5.0 SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574MX-5.0/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
LM2574MX-ADJ/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com 24-Aug-2017
*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2574HVMX-12/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574HVMX-15/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574HVMX-3.3/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574HVMX-5.0 SOIC NPA 14 1000 367.0 367.0 38.0
LM2574HVMX-5.0/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574HVMX-ADJ/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574MX-12/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574MX-3.3/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574MX-5.0 SOIC NPA 14 1000 367.0 367.0 38.0
LM2574MX-5.0/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
LM2574MX-ADJ/NOPB SOIC NPA 14 1000 367.0 367.0 38.0
Pack Materials-Page 2
MECHANICAL DATA
NPA0014B
www.ti.com
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Copyright © 2017, Texas Instruments Incorporated

LM2574x SIMPLE SWITCHER® 0.5-A Step-Down Voltage Regulator: 1 Features 3 Description

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LM2574x SIMPLE SWITCHER® 0.5-A Step-Down Voltage Regulator

Typical Application (Fixed Output Voltage Versions)

Changes from Revision B (November 2004) to Revision C Page

• Changed layout of National Data Sheet to TI format ............................................................................................................. 1

2 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated

Product Folder Links: LM2574 LM2574HV

5 Pin Configuration and Functions

Copyright © 1999–2016, Texas Instruments Incorporated Submit Documentation Feedback 3

6.2 ESD Ratings

6.3 Recommended Operating Conditions

6.4 Thermal Information

4 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated

Product Folder Links: LM2574 LM2574HV

6.5 Electrical Characteristics for All Output Voltage Versions

6.6 Electrical Characteristics – 3.3-V Version

(1) Test Circuit in Figure 22 and Figure 27.

Copyright © 1999–2016, Texas Instruments Incorporated Submit Documentation Feedback 5

6.7 Electrical Characteristics – 5-V Version

(1) Test circuit in Figure 22 and Figure 27.

6.8 Electrical Characteristics – 12-V Version

(1) Test circuit in Figure 22 and Figure 27.

6.9 Electrical Characteristics – 15-V Version

(1) Test circuit in Figure 22 and Figure 27.

6 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated

Product Folder Links: LM2574 LM2574HV

6.10 Electrical Characteristics – Adjustable Version

(1) Test circuit in Figure 22 and Figure 27.

Copyright © 1999–2016, Texas Instruments Incorporated Submit Documentation Feedback 7

6.11 Typical Characteristics

Figure 1. Normalized Output Voltage Figure 2. Line Regulation

Figure 3. Dropout Voltage Figure 4. Current Limit

Figure 5. Supply Current Figure 6. Standby Quiescent Current

8 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated

Product Folder Links: LM2574 LM2574HV

Typical Characteristics (continued)

Figure 7. Oscillator Frequency Figure 8. Switch Saturation Voltage

Figure 9. Efficiency Figure 10. Minimum Operating Voltage

Copyright © 1999–2016, Texas Instruments Incorporated Submit Documentation Feedback 9

Typical Characteristics (continued)

10 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated

Product Folder Links: LM2574 LM2574HV

7.2 Functional Block Diagram

Copyright © 2016, Texas Instruments Incorporated

7.3 Feature Description

7.3.2 Undervoltage Lockout

Copyright © 1999–2016, Texas Instruments Incorporated Submit Documentation Feedback 11

Feature Description (continued)

Note: Complete circuit not shown (see Figure 20).

Figure 15. Undervoltage Lockout for Buck Circuit

Note: Complete circuit not shown (see Figure 20).

Figure 16. Undervoltage Lockout for Buck-Boost Circuit

7.3.3 Delayed Start-Up

7.3.4 Adjustable Output, Low-Ripple Power Supply

12 Submit Documentation Feedback Copyright © 1999–2016, Texas Instruments Incorporated

Product Folder Links: LM2574 LM2574HV

Feature Description (continued)

Note: Complete circuit not shown.