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LM2733
SNVS209F – NOVEMBER 2002 – REVISED DECEMBER 2014

LM2733 0.6 and 1.6-MHz Boost Converters With 40-V Internal FET Switch in SOT-23
1 Features 3 Description
•
1 40-V DMOS FET Switch The LM2733 switching regulators are current-mode
boost converters operating fixed frequency of 1.6
• 1.6 MHz (“X”), 0.6 MHz (“Y”) Switching Frequency MHz (“X” option) and 600 kHz (“Y” option).
• Low RDS(ON) DMOS FET
The use of SOT-23 package, made possible by the
• Switch Current up to 1A minimal power loss of the internal 1-A switch, and
• Wide Input Voltage Range (2.7 V – 14 V) use of small inductors and capacitors result in the
• Low Shutdown Current (< 1 µA) industry's highest power density. The 40-V internal
switch makes these solutions perfect for boosting to
• 5-Lead SOT-23 Package
voltages of 16 V or greater.
• Uses Tiny Capacitors and Inductors
These parts have a logic-level shutdown pin that can
• Cycle-by-Cycle Current Limiting
be used to reduce quiescent current and extend
• Internally Compensated battery life.
Protection is provided through cycle-by-cycle current
2 Applications limiting and thermal shutdown. Internal compensation
• White LED Current Source simplifies design and reduces component count.
• PDA’s and Palm-Top Computers
Device Information(1)
• Digital Cameras
PART NUMBER PACKAGE BODY SIZE (NOM)
• Portable Phones and Games
LM2733 SOT-23 (5) 2.90 mm x 1.60 mm
• Local Boost Regulator
(1) For all available packages, see the orderable addendum at
the end of the datasheet.

Typical Application Circuit Efficiency vs. Load Current

D1
L1/10PH MBR0520
5 VIN
VIN U1 SW
R3 12V
LM2733 ³;´ R1/117K
51K OUT
SHDN FB
SHDN 330mA
GND (TYP)
C1
R2 CF C2
2.2PF 220pF
GND 13.3K 4.7PF

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.
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Table of Contents
1 Features .................................................................. 1 7.3 Feature Description................................................. 10
2 Applications ........................................................... 1 7.4 Device Functional Modes........................................ 11
3 Description ............................................................. 1 8 Application and Implementation ........................ 12
4 Revision History..................................................... 2 8.1 Application Information............................................ 12
8.2 Typical Application .................................................. 12
5 Pin Configuration and Functions ......................... 3
6 Specifications......................................................... 3 9 Power Supply Recommendations...................... 18
6.1 Absolute Maximum Ratings ...................................... 3 10 Layout................................................................... 18
6.2 ESD Ratings.............................................................. 3 10.1 Layout Guidelines ................................................. 18
6.3 Recommended Operating Conditions....................... 4 10.2 Layout Example .................................................... 18
6.4 Thermal Information .................................................. 4 11 Device and Documentation Support ................. 19
6.5 Electrical Characteristics........................................... 4 11.1 Trademarks ........................................................... 19
6.6 Typical Characteristics .............................................. 6 11.2 Electrostatic Discharge Caution ............................ 19
7 Detailed Description ............................................ 10 11.3 Glossary ................................................................ 19
7.1 Overview ................................................................. 10 12 Mechanical, Packaging, and Orderable
7.2 Functional Block Diagram ....................................... 10 Information ........................................................... 19

4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision E (April 2013) to Revision F Page

• Added Pin Configuration and Functions section, 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

Changes from Revision D (April 2013) to Revision E Page

• Changed layout of National Data Sheet to TI format ........................................................................................................... 11

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5 Pin Configuration and Functions

5-Pin
SOT-23 Package
Top View

Pin Functions
PIN
I/O DESCRIPTION
NAME NO.
SW 1 O Drain of the internal FET switch.
GND 2 GND Analog and power ground.
FB 3 I Feedback point that connects to external resistive divider.
SHDN 4 I Shutdown control input. Connect to VIN if this feature is not used.
VIN 5 I Analog and power input.

6 Specifications
6.1 Absolute Maximum Ratings (1) (2)
MIN MAX UNIT
Input Supply Voltage (VIN) −0.4 14.5 V
FB Pin Voltage −0.4 6 V
SW Pin Voltage −0.4 40 V
SHDN Pin Voltage −0.4 VIN + 0.3 V
Power Dissipation (3) Internally Limited
Lead Temp. (Soldering, 5 sec.) 300 °C
Tstg Storage temperature −65 150 °C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply
when operating the device outside of the limits set forth under the operating ratings which specify the intended range of operating
conditions.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) The maximum power dissipation which can be safely dissipated for any application is a function of the maximum junction temperature,
TJ(MAX) = 125°C, the junction-to-ambient thermal resistance for the SOT-23 package, θJ-A = 265°C/W, and the ambient temperature,
TA. The maximum allowable power dissipation at any ambient temperature for designs using this device can be calculated using the

formula: If power dissipation exceeds the maximum specified above, the internal thermal protection
circuitry will protect the device by reducing the output voltage as required to maintain a safe junction temperature.

6.2 ESD Ratings

VALUE UNIT
(1)
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins ±2000
V(ESD) Electrostatic discharge V
Machine model ±200

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

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6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)
MIN MAX UNIT
Input Supply Voltage (VIN) 2.7 14.0 V
SHDN Pin Voltage 0 VIN V
Junction Temperature Range −40 125 °C

6.4 Thermal Information

LM2733
THERMAL METRIC (1) DBV UNIT
5 PINS
RθJA Junction-to-ambient thermal resistance 210
RθJC(top) Junction-to-case (top) thermal resistance 122
RθJB Junction-to-board thermal resistance 38.4
°C/W
ψJT Junction-to-top characterization parameter 12.8
ψJB Junction-to-board characterization parameter 37.5
RθJC(bot) Junction-to-case (bottom) thermal resistance n/a

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

6.5 Electrical Characteristics

Unless otherwise specified: VIN = 5 V, VSHDN = 5 V, IL = 0A, TJ = 25°C.
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
VIN Input Voltage −40°C ≤ TJ ≤ +125°C 2.7 14 V
ISW Switch Current Limit See (3) 1.0 1.5 A
RDS(ON) Switch ON Resistance ISW = 100 mA 500 650 mΩ
SHDNTH Shutdown Threshold Device ON, −40°C ≤ TJ ≤ +125°C 1.5
Device OFF, −40°C ≤ TJ ≤ 0.50 V
+125°C
ISHDN Shutdown Pin Bias Current VSHDN = 0 0
VSHDN = 5 V 0
µA
VSHDN = 5 V, −40°C ≤ TJ ≤ 2
+125°C
VFB Feedback Pin Reference Voltage VIN = 3 V 1.230
V
VIN = 3 V, −40°C ≤ TJ ≤ +125°C 1.205 1.255
IFB Feedback Pin Bias Current VFB = 1.23 V 60 nA
IQ Quiescent Current VSHDN = 5 V, Switching "X" 2.1
VSHDN = 5 V, Switching "X", 3.0
−40°C ≤ TJ ≤ +125°C
mA
VSHDN = 5 V, Switching "Y" 1.1
VSHDN = 5 V, Switching "Y", 2
−40°C ≤ TJ ≤ +125°C
VSHDN = 5 V, Not Switching 400
VSHDN = 5 V, Not Switching, 500
µA
−40°C ≤ TJ ≤ +125°C
VSHDN = 0 0.024 1
Δ VFBΔVIN FB Voltage Line Regulation 2.7 V ≤ VIN ≤ 14 V 0.02 %/V

(1) Limits are specified by testing, statistical correlation, or design.

(2) Typical values are derived from the mean value of a large quantity of samples tested during characterization and represent the most
likely expected value of the parameter at room temperature.
(3) Switch current limit is dependent on duty cycle (see Typical Performance Characteristics). Limits shown are for duty cycles ≤ 50%.
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Electrical Characteristics (continued)

Unless otherwise specified: VIN = 5 V, VSHDN = 5 V, IL = 0A, TJ = 25°C.
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
FSW Switching Frequency “X” Option 1.6
“X” Option, −40°C ≤ TJ ≤ +125°C 1.15 1.85
MHz
“Y” Option 0.60
“Y” Option, −40°C ≤ TJ ≤ +125°C 0.40 0.8
DMAX Maximum Duty Cycle “X” Option 93%
“X” Option, −40°C ≤ TJ ≤ +125°C 87%
“Y” Option 96%
“Y” Option, −40°C ≤ TJ ≤ +125°C 93%
IL Switch Leakage Not Switching VSW = 5 V 1 µA

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6.6 Typical Characteristics

Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.

1.06

1.05

1.04

Iq ACTIVE (mA)
1.03

1.02

1.01

0.99

0.98
-50 -25 0 25 50 75 100 125 150

o
TEMPERATURE ( C)

Figure 2. Iq VIN (Active) vs Temperature - "Y"

Figure 1. Iq VIN (Active) vs Temperature - "X"
0.615

0.610

OSCILLATOR FREQUENCY (MHz) 0.605

0.600

0.595

0.590

0.585

0.580

0.575
-50 -25 0 25 50 75 100 125 150

TEMPERATURE (oC)

Figure 3. Oscillator Frequency vs Temperature - "X" Figure 4. Oscillator Frequency vs Temperature - "Y"
93.4 96.55
96.5
93.3
96.45
93.2
MAX DUTY CYCLE
MAX DUTY CYCLE (%)

96.4

93.1 96.35
96.3
93.0
96.25

92.9 96.2
96.15
92.8
96.1
92.7 96.05
-40 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 125 150

TEMPERATURE (oC) TEMPERATURE (oC)

Figure 5. Max. Duty Cycle vs Temperature - "X" Figure 6. Max. Duty Cycle vs Temperature - "Y"

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Typical Characteristics (continued)

Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.

Figure 7. Feedback Voltage vs Temperature Figure 8. RDS(ON) vs Temperature

Figure 9. Current Limit vs Temperature Figure 10. RDS(ON) vs VIN

100
90

80 VIN = 10V
VIN = 5V
70
EFFICIENCY (%)

60
VIN = 3.3V
50
40
30
20

10
0
0 200 400 600 800 1000

LOAD CURRENT (mA)

Figure 11. Efficiency vs Load Current (VOUT = 12 V) - "X" Figure 12. Efficiency vs Load Current (VOUT = 15 V) - "X"

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Typical Characteristics (continued)

Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.
100 100
90 90
80 VIN = 10V VIN = 10V
80

EFFICIENCY (%)
VIN = 5V
EFFICIENCY (%)

70 70 VIN = 5V
60 VIN = 3.3V 60
50 50
40 40
30 30
20 20
10 10
0 0
0 100 200 300 400 500 600 700 0 50 100 150 200 250 300 350 400
LOAD CURRENT (mA) LOAD CURRENT (mA)

Figure 13. Efficiency vs Load Current (VOUT = 20 V) - "X" Figure 14. Efficiency vs Load Current (VOUT = 25 V) - "X"
100 100
90 90
80 VIN = 10V 80 VIN = 10V
EFFICIENCY (%)

70
EFFICIENCY (%)
70
60 VIN = 5V
60
50 50
40 40
30 30
20 20
10
10
0
0
0 50 100 150 200 250 300 350 0 50 200
100 150
LOAD CURRENT (mA) LOAD CURRENT (mA)

Figure 15. Efficiency vs Load Current (VOUT = 30 V) - "X" Figure 16. Efficiency vs Load Current (VOUT = 35 V) - "X"
90

80
VIN=10V
70
EFFICIENCY (%)

60

50

40

30

20

10

0
0 50 100 150 200

LOAD CURRENT (mA)

Figure 17. Efficiency vs Load Current (VOUT = 40 V) - "X" Figure 18. Efficiency vs Load (VOUT = 15 V) - "Y"

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Typical Characteristics (continued)

Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.

Figure 19. Efficiency vs Load (VOUT = 20 V) - "Y" Figure 20. Efficiency vs Load (VOUT = 25 V) - "Y"

Figure 21. Efficiency vs Load (VOUT = 30 V) - "Y" Figure 22. Efficiency vs Load (VOUT = 35 V) - "Y"

Figure 23. Efficiency vs Load (VOUT = 40 V) - "Y"

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7 Detailed Description

7.1 Overview
The LM2733 device is a switching converter IC that operates at a fixed frequency (0.6 or 1.6 MHz) using current-
mode control for fast transient response over a wide input voltage range and incorporate pulse-by-pulse current
limiting protection. Because this is current mode control, a 50 mΩ sense resistor in series with the switch FET is
used to provide a voltage (which is proportional to the FET current) to both the input of the pulse width
modulation (PWM) comparator and the current limit amplifier.
At the beginning of each cycle, the S-R latch turns on the FET. As the current through the FET increases, a
voltage (proportional to this current) is summed with the ramp coming from the ramp generator and then fed into
the input of the PWM comparator. When this voltage exceeds the voltage on the other input (coming from the
Gm amplifier), the latch resets and turns the FET off. Since the signal coming from the Gm amplifier is derived
from the feedback (which samples the voltage at the output), the action of the PWM comparator constantly sets
the correct peak current through the FET to keep the output volatge in regulation.
Q1 and Q2 along with R3 - R6 form a bandgap voltage reference used by the IC to hold the output in regulation.
The currents flowing through Q1 and Q2 will be equal, and the feedback loop will adjust the regulated output to
maintain this. Because of this, the regulated output is always maintained at a voltage level equal to the voltage at
the FB node "multiplied up" by the ratio of the output resistive divider.
The current limit comparator feeds directly into the flip-flop, that drives the switch FET. If the FET current reaches
the limit threshold, the FET is turned off and the cycle terminated until the next clock pulse. The current limit
input terminates the pulse regardless of the status of the output of the PWM comparator.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Switching Frequency
The LM2733 device is provided with two switching frequencies: the “X” version is typically 1.6 MHz, while the “Y”
version is typically 600 kHz. The best frequency for a specific application must be determined based on the
tradeoffs involved. See Switching Frequency in the Detailed Design Procedure section.

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7.4 Device Functional Modes

7.4.1 Shutdown Pin Operation
The device is turned off by pulling the shutdown pin low. If this function is not going to be used, the pin should be
tied directly to VIN. If the SHDN function will be needed, a pull-up resistor must be used to VIN (approximately
50k-100kΩ recommended). The SHDN pin must not be left unterminated.

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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

The LM2733 device is a high frequency switching boost regulator that offers small size and high power
conversion efficiency. The "X" version of the part operates at 1.6 MHz switching frequency and the "Y" version at
600 kHz.
The LM2733 device targets applications with high output voltages and uses a high voltage FET allowing switch
currents up to 1 A. The LM2731 device is similar to the LM2733 device but has a lower voltage FET allowing
switch currents up to 1.8 A.

8.2 Typical Application

Figure 24. Basic Application Circuit

8.2.1 Design Requirements

Table 1. Circuit Configurations

LM2733-X LM2733-X LM2733-Y
Component
Low Voltage 5-12V 330mA typ High Voltage 20V 170mA typ. High Voltage 30V 110mA typ
R1 117K 205K 309K
R2 13.3K 13.3K 13.3K
Cf 220pF 120pF 82pF
D1 MBR0520 MBR0530 MBR0540

8.2.2 Detailed Design Procedure

8.2.2.1 Selecting the External Capacitors

The best capacitors for use with the LM2733 device are multi-layer ceramic capacitors. They have the lowest
ESR (equivalent series resistance) and highest resonance frequency which makes them optimum for use with
high frequency switching converters.
When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as
Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage,
they may provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor
manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from
Taiyo-Yuden, AVX, and Murata.

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8.2.2.2 Selecting the Output Capacitor

A single ceramic capacitor of value 4.7 µF to 10 µF will provide sufficient output capacitance for most
applications. For output voltages below 10V, a 10 µF capacitance is required. If larger amounts of capacitance
are desired for improved line support and transient response, tantalum capacitors can be used in parallel with the
ceramics. Aluminum electrolytics with ultra low ESR such as Sanyo Oscon can be used, but are usually
prohibitively expensive. Typical AI electrolytic capacitors are not suitable for switching frequencies above 500
kHz due to significant ringing and temperature rise due to self-heating from ripple current. An output capacitor
with excessive ESR can also reduce phase margin and cause instability.

8.2.2.3 Selecting the Input Capacitor

An input capacitor is required to serve as an energy reservoir for the current which must flow into the coil each
time the switch turns ON. This capacitor must have extremely low ESR, so ceramic is the best choice. We
recommend a nominal value of 2.2 µF, but larger values can be used. Since this capacitor reduces the amount of
voltage ripple seen at the input pin, it also reduces the amount of EMI passed back along that line to other
circuitry.

8.2.2.4 Feed-Forward Compensation

Although internally compensated, the feed-forward capacitor Cf is required for stability (see Figure 24). Adding
this capacitor puts a zero in the loop response of the converter. Without it, the regulator loop can oscillate. The
recommended frequency for the zero fz should be approximately 8 kHz. Cf can be calculated using the formula:
Cf = 1 / (2 X π X R1 X fz) (1)

8.2.2.5 Selecting Diodes

The external diode used in the typical application should be a Schottky diode. If the switch voltage is less than 15
V, a 20 V diode such as the MBR0520 is recommended. If the switch voltage is between 15 V and 25 V, a 30-V
diode such as the MBR0530 is recommended. If the switch voltage exceeds 25 V, a 40-V diode such as the
MBR0540 should be used.
The MBR05XX series of diodes are designed to handle a maximum average current of 0.5 A. For applications
exceeding 0.5 A average but less than 1 A, a Microsemi UPS5817 can be used.

8.2.2.6 Setting the Output Voltage

The output voltage is set using the external resistors R1 and R2 (see Figure 24). A value of approximately 13.3
kΩ is recommended for R2 to establish a divider current of approximately 92 µA. R1 is calculated using the
formula:
R1 = R2 X (VOUT/1.23 − 1) (2)

8.2.2.7 Switching Frequency

The device options provide for two fixed frequency operating conditions 1.6 MHz, and 600 kHz. Chose the
operating frequency required noting the following trade-offs:
Higher switching frequency means the inductors and capacitors can be made smaller and cheaper for a given
output voltage and current. The down side is that efficiency is slightly lower because the fixed switching losses
occur more frequently and become a larger percentage of total power loss. EMI is typically worse at higher
switching frequencies because more EMI energy will be seen in the higher frequency spectrum where most
circuits are more sensitive to such interference.

8.2.2.8 Duty Cycle

The maximum duty cycle of the switching regulator determines the maximum boost ratio of output-to-input
voltage that the converter can attain in continuous mode of operation. The duty cycle for a given boost
application is defined as:
VOUT + VDIODE - VIN
Duty Cycle =
VOUT + VDIODE - VSW (3)
This applies for continuous mode operation.

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The equation shown for calculating duty cycle incorporates terms for the FET switch voltage and diode forward
voltage. The actual duty cycle measured in operation will also be affected slightly by other power losses in the
circuit such as wire losses in the inductor, switching losses, and capacitor ripple current losses from self-heating.
Therefore, the actual (effective) duty cycle measured may be slightly higher than calculated to compensate for
these power losses. A good approximation for effective duty cycle is :
DC (eff) = (1 - Efficiency x (VIN/VOUT)) (4)
Where the efficiency can be approximated from the curves provided.

8.2.2.9 Inductance Value

The first question we are usually asked is: “How small can I make the inductor?” (because they are the largest
sized component and usually the most costly). The answer is not simple and involves tradeoffs in performance.
Larger inductors mean less inductor ripple current, which typically means less output voltage ripple (for a given
size of output capacitor). Larger inductors also mean more load power can be delivered because the energy
stored during each switching cycle is:
E =L/2 X (lp)2 (5)
Where “lp” is the peak inductor current. An important point to observe is that the LM2733 device will limit its
switch current based on peak current. This means that since lp (maximum) is fixed, increasing L will increase the
maximum amount of power available to the load. Conversely, using too little inductance may limit the amount of
load current which can be drawn from the output.
Best performance is usually obtained when the converter is operated in “continuous” mode at the load current
range of interest, typically giving better load regulation and less output ripple. Continuous operation is defined as
not allowing the inductor current to drop to zero during the cycle. It should be noted that all boost converters shift
over to discontinuous operation as the output load is reduced far enough, but a larger inductor stays “continuous”
over a wider load current range.
To better understand these tradeoffs, a typical application circuit (5V to 12V boost with a 10 µH inductor) will be
analyzed. We will assume:
VIN = 5 V, VOUT = 12 V, VDIODE = 0.5 V, VSW = 0.5 V
Since the frequency is 1.6 MHz (nominal), the period is approximately 0.625 µs. The duty cycle will be 62.5%,
which means the ON time of the switch is 0.390 µs. It should be noted that when the switch is ON, the voltage
across the inductor is approximately 4.5 V.
Using the equation:
V = L (di/dt) (6)
We can then calculate the di/dt rate of the inductor which is found to be 0.45 A/µs during the ON time. Using
these facts, we can then show what the inductor current will look like during operation:

Figure 25. 10-µH Inductor Current,

5-V – 12-V Boost (LM2733X)

During the 0.390 µs ON time, the inductor current ramps up 0.176 A and ramps down an equal amount during
the OFF time. This is defined as the inductor “ripple current”. It can also be seen that if the load current drops to
about 33 mA, the inductor current will begin touching the zero axis which means it will be in discontinuous mode.
A similar analysis can be performed on any boost converter, to make sure the ripple current is reasonable and
continuous operation will be maintained at the typical load current values.

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8.2.2.10 Maximum Switch Current

The maximum FET swtch current available before the current limiter cuts in is dependent on duty cycle of the
application. This is illustrated in the graphs below which show both the typical and specified values of switch
current for both the "X" and "Y" versions as a function of effective (actual) duty cycle:

1600 1600

1400 1400

SWITCH CURRENT LIMIT (mA)

VIN = 5V
VIN = 5V
SWITCH CURRENT LIMIT (mA)

1200 1200
VIN = 3.3V
1000 VIN = 3.3V 1000

800 800
VIN = 2.7V
VIN = 2.7V
600 600

400 400

200 200

0 0
0 20 40 60 80 100 0 20 40 60 80 100

DUTY CYCLE (%) = [1 - EFF*(VIN/VOUT))] DUTY CYCLE (%) = [1 - EFF*(VIN/VOUT))]

Figure 26. Switch Current Limit vs Duty Cycle - "X" Figure 27. Switch Current Limit vs Duty Cycle - "Y"

8.2.2.11 Calculating Load Current

As shown in the figure which depicts inductor current, the load current is related to the average inductor current
by the relation:
ILOAD = IIND(AVG) x (1 - DC) (7)
Where "DC" is the duty cycle of the application. The switch current can be found by:
ISW = IIND(AVG) + ½ (IRIPPLE) (8)
Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency:
IRIPPLE = DC x (VIN-VSW) / (f x L) (9)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
ILOAD(max) = (1 - DC) x (ISW(max) - DC (VIN - VSW))
2fL (10)
The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-OFF
switching losses of the FET and diode. For actual load current in typical applications, we took bench data for
various input and output voltages for both the "X" and "Y" versions of the LM2733 device and displayed the
maximum load current available for a typical device in graph form:

Figure 28. Max. Load Current vs VIN - "X" Figure 29. Max. Load Current vs VIN - "Y"

Copyright © 2002–2014, Texas Instruments Incorporated Submit Documentation Feedback 15

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8.2.2.12 Design Parameters VSW and ISW

The value of the FET "ON" voltage (referred to as VSW in the equations) is dependent on load current. A good
approximation can be obtained by multiplying the "ON Resistance" of the FET times the average inductor
current.
FET on resistance increases at VIN values below 5 V, since the internal N-FET has less gate voltage in this input
voltage range (see Typical Characteristics). Above VIN = 5 V, the FET gate voltage is internally clamped to 5 V.
The maximum peak switch current the device can deliver is dependent on duty cycle. The minimum value is
specified to be > 1 A at duty cycle below 50%. For higher duty cycles, see Typical Characteristics.

8.2.2.13 Thermal Considerations

At higher duty cycles, the increased ON time of the FET means the maximum output current will be determined
by power dissipation within the LM2733 FET switch. The switch power dissipation from ON-state conduction is
calculated by:
P(SW) = DC x IIND(AVE)2 x RDSON (11)
There will be some switching losses as well, so some derating needs to be applied when calculating IC power
dissipation.

8.2.2.14 Minimum Inductance

In some applications where the maximum load current is relatively small, it may be advantageous to use the
smallest possible inductance value for cost and size savings. The converter will operate in discontinuous mode in
such a case.
The minimum inductance should be selected such that the inductor (switch) current peak on each cycle does not
reach the 1-A current limit maximum. To understand how to do this, an example will be presented.
In the example, the LM2733X will be used (nominal switching frequency 1.6 MHz, minimum switching frequency
1.15 MHz). This means the maximum cycle period is the reciprocal of the minimum frequency:
TON(max) = 1/1.15M = 0.870 µs (12)
We will assume the input voltage is 5 V, VOUT = 12 V, VSW = 0.2 V, VDIODE = 0.3 V. The duty cycle is:
Duty Cycle = 60.3%
Therefore, the maximum switch ON time is 0.524 µs. An inductor should be selected with enough inductance to
prevent the switch current from reaching 1A in the 0.524 µs ON time interval (see below):

Figure 30. Discontinuous Design, 5V–12V Boost (LM2733X)

The voltage across the inductor during ON time is 4.8V. Minimum inductance value is found by:
V = L X dl/dt, L = V X (dt/dl) = 4.8 (0.524µ/1) = 2.5 µH (13)
In this case, a 2.7 µH inductor could be used assuming it provided at least that much inductance up to the 1A
current value. This same analysis can be used to find the minimum inductance for any boost application. Using
the slower switching “Y” version requires a higher amount of minimum inductance because of the longer
switching period.

8.2.2.15 Inductor Suppliers

Some of the recommended suppliers of inductors for this product include, but not limited to are Sumida, Coilcraft,
Panasonic, TDK and Murata. When selecting an inductor, make certain that the continuous current rating is high
enough to avoid saturation at peak currents. A suitable core type must be used to minimize core (switching)
losses, and wire power losses must be considered when selecting the current rating.

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 LM2733
www.ti.com SNVS209F – NOVEMBER 2002 – REVISED DECEMBER 2014

8.2.3 Application Curves

Figure 31. Efficiency vs. Load Current (5-12V, X-version) Figure 32. Efficiency vs. Load Current (5-20V X-version)

Figure 33. Efficiency vs. Load Current (5 - 30V Y-version)

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LM2733
SNVS209F – NOVEMBER 2002 – REVISED DECEMBER 2014 www.ti.com

9 Power Supply Recommendations

The device input voltage range is 2.7 V to 14 V.
The voltage on the shutdown pin should not exceed the voltage on the VIN pin. For applications that do not
require a shutdown function the shutdown pin may be connected to the VIN pin. In this case a 47-KΩ resistor is
recommended to be connected between these pins.

10 Layout

10.1 Layout Guidelines

High frequency switching regulators require very careful layout of components in order to get stable operation
and low noise. All components must be as close as possible to the LM2733 device. It is recommended that a 4-
layer PCB be used so that internal ground planes are available.
Some additional guidelines to be observed:
1. Keep the path between L1, D1, and C2 extremely short. Parasitic trace inductance in series with D1 and C2
will increase noise and ringing.
2. The feedback components R1, R2 and CF must be kept close to the FB pin of U1 to prevent noise injection
on the FB pin trace.
3. If internal ground planes are available (recommended) use vias to connect directly to ground at pin 2 of U1,
as well as the negative sides of capacitors C1 and C2.

10.2 Layout Example

Figure 34. Recommended PCB Component Layout

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 LM2733
www.ti.com SNVS209F – NOVEMBER 2002 – REVISED DECEMBER 2014

11 Device and Documentation Support

11.1 Trademarks
All trademarks are the property of their respective owners.
11.2 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.

11.3 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.

Copyright © 2002–2014, Texas Instruments Incorporated Submit Documentation Feedback 19

Product Folder Links: LM2733
 PACKAGE OPTION ADDENDUM

www.ti.com 23-Oct-2014

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)

LM2733XMF NRND SOT-23 DBV 5 1000 TBD Call TI Call TI -40 to 125 S52A
LM2733XMF/NOPB ACTIVE SOT-23 DBV 5 1000 Green (RoHS CU SN Level-1-260C-UNLIM -40 to 125 S52A
& no Sb/Br)
LM2733XMFX/NOPB ACTIVE SOT-23 DBV 5 3000 Green (RoHS CU SN Level-1-260C-UNLIM -40 to 125 S52A
& no Sb/Br)
LM2733YMF NRND SOT-23 DBV 5 1000 TBD Call TI Call TI -40 to 125 S52B
LM2733YMF/NOPB ACTIVE SOT-23 DBV 5 1000 Green (RoHS CU SN Level-1-260C-UNLIM -40 to 125 S52B
& no Sb/Br)
LM2733YMFX/NOPB ACTIVE SOT-23 DBV 5 3000 Green (RoHS CU SN Level-1-260C-UNLIM -40 to 125 S52B
& no Sb/Br)

(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.
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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)

(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.

Addendum-Page 1
 PACKAGE OPTION ADDENDUM

www.ti.com 23-Oct-2014

(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 2
 PACKAGE MATERIALS INFORMATION

www.ti.com 22-Jul-2015

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)
LM2733XMF SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2733XMF/NOPB SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2733XMFX/NOPB SOT-23 DBV 5 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2733YMF SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2733YMF/NOPB SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2733YMFX/NOPB SOT-23 DBV 5 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

Pack Materials-Page 1
 PACKAGE MATERIALS INFORMATION

www.ti.com 22-Jul-2015

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2733XMF SOT-23 DBV 5 1000 210.0 185.0 35.0
LM2733XMF/NOPB SOT-23 DBV 5 1000 210.0 185.0 35.0
LM2733XMFX/NOPB SOT-23 DBV 5 3000 210.0 185.0 35.0
LM2733YMF SOT-23 DBV 5 1000 210.0 185.0 35.0
LM2733YMF/NOPB SOT-23 DBV 5 1000 210.0 185.0 35.0
LM2733YMFX/NOPB SOT-23 DBV 5 3000 210.0 185.0 35.0

Pack Materials-Page 2
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