3A L.D.O.

VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

TO-220 PKG
FEATURES

● Output Current of 3A
● Fast Transient Response
● 0.04% Line Regulation
● 0.2% Load Regulation
1 3
● Internal Thermal and Current Limiting
● Adjustable or Fixed Output Voltage(1.5V, 1.8V, 2.5V, 3.3V, 5.0V) TO-252 PKG
● Surface Mount Package TO220-3LD & TO-263-3LD
● 100% Thermal Limit Burn-in
● Low Dropout Voltage 1.5V at 3A Output Current
● Moisture Sensitivity Level 3

TO-263 PKG
APPLICATIONS

● High Efficiency Linear Regulators / Power Supply 1

● High Efficiency "Green" Computer Systems 3
● Constant Current Regulators 1. Adj/Gnd 2. Output 3. Input
● Portable Instrumentation
● SMPS Post-Regulator ORDERING INFORMATION
● Adjustable Power Supplies Device & Marking Package
● Powering LM1085T-X.X TO-220-3LD
LM1085RS-XX TO252-3LD
LM1085R-X.X TO263-3LD
DESCRIPTION (XX = Vout = 1.5V, 1.8V, 2.5V, 3.3V, 5.0V
Adjustable= ADJ)
The LM1085 series of positive adjustable and fixed regulators are designed to provide 3A with
high efficient. All internal circuitry is designed to operate down to 1.4V input to output differential.
On-chip trimming adjusts the reference voltage to 1%.
It's low dropout voltage and fast transient response make it ideal for low voltage microprocessor
applications. Internal current and thermal limiting provides protection against any overload condition
that would create excessive junction temperature.

TEST & TYPICAL APPLICATION CIRCUIT

LM1085 LM1085
3.3V ADJ

Note
VREF=VOUT-VADJ=1.25V(Typ.)
(1) C1 Needed if device is far away from filter capacitors. VOUT=VREFx(1+RF2/RF1)+IADJxRF2
(2) C2 minimum value required for stability IADJ=55㎂(Typ.)

2008 - Ver 1.0 HTC

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

BLOCK DIAGRAM

ABSOULTE MAXIMUM RATINS

CHARACTERISTIC SYMBOL VALUE UNIT

Supply Voltage Vin 12 V

Operating Junction Temperature Range Topr -10 ~ 70 ℃

Storage Temperature Range Tstg -65 ~ 150 ℃

Thermal Resistance Junction to Case TO-263 Tjc 3 C/W

Thermal Resistance Junction to Ambient TO-263 Tja 60 C/W

Lead Temperature (Soldering) 10 sec. Tsol 300 ℃

Maximum Output Current Imax 3 A

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

ELECTRICAL CHARACTERISTICS I OUT =100㎃, TA=25℃, unless otherwise specified

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

1.5V Version

Output Voltage 0<IOUT<3A, 2.75V<V IN 1.485 1.5 1.515 V

1.8V Version

Output Voltage 0<IOUT<3A, 2.75V<V IN 1.78 1.8 1.82 V

2.5V Version

Output Voltage 0<IOUT<3A, 3.5V<V IN 2.475 2.5 2.525 V

3.3V Version

Output Voltage 0<IOUT<3A, 4.75V<V IN 3.267 3.3 3.333 V

5.0V Version

Output Voltage 0≤IOUT≤3A, 5.5V≤VIN 4.95 5 5.05 V

All Voltage Options

VIN≤7V,P≤PMAX 1.238 1.25 1.263

Reference Voltage (V REF) V
1.5V≤(VIN-VOUT)≤5.75V, 10㎃≤IOUT≤3A 1.225 1.25 1.27

Min. Load Current(Note 3) 1.5V≤(VIN-VOUT)≤5.75V 5 13 mA

Line Regulation (ΔV REF(VIN)) 2.75V≤VIN≤7V, IOUT=10㎃, TJ=25℃ 0.05 0.3 %

Load Regulation (ΔV REF(VOUT)) 10㎃≤IOUT≤3A,(VIN-VOUT)=3V,TJ=25℃ 0.1 0.4 %

Dropout Voltage ΔVREF=1% , Iout=3A 1.2 1.4 V

Current Limit Vin-Vout=3V

3.2 4.5 A
IOUT(MAX) 1.4V≤(VIN-VOUT) Adjustable Only

Long Term Stability TA=125℃, 1000Hrs 0.3 1 %

Thermal Regulation
TA=25℃, 30㎳ pulse 0.01 0.02 %/W
(ΔVOUT(Pwr))

Output Noise, RMS 10Hz to 10Khz TA=25℃ 0.003 %/Vo

Junction to Tab 3
Thermal Resistance ℃/W
Junction to Ambient 60

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085
TYPICAL PERFORMANCE CHARACTERISTICS

Figure 1. Dropout Voltage vs Output Current Figure 2. Reference Voltage vs Temperature

Figure 3. Load Regulation vs. Output Current Figure 4. Minimum Load Current

Figure 5. Adjust Pin Current vs Temperature Figure 6. Ripple Rejection vs. Frequency

(Fixed Versions)

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

Figure 9. Ripple Rejection vs. Frequency (Adjustable Versions)

APPLICATIONS INFORMATION

LM1085-ADJ

ADJ

Figure 10. Resistor Divider Scheme for the Adjustable Version

LM1085-XX

Figure 11. Protection Diode Scheme for Fixed Output Regulators

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

APPLICATION INFORMATION

The LM1085 series of adjustable and fixed regulators are easy to use and have all the protection
features expected in high performance voltage regulators : short circuit protection and thermal
shut-down. Pin compatible with older three terminal adjustable regulators, these devices offer the
advantage of a lower dropout voltage, more precies reference tolerance and improved reference
stability with temperature.

STABILITY

The circuit design used in the LM1085 series requires the use of an output capacitor as part of
the device frequency compensation.
The addition of 150uF aluminum electrolytic or a 22uF solid tantalum on the output will ensure
stability for all operating conditions. When the adjustment terminal is bypassed with a capacitor to
improve the ripple rejection, the requirement for an output capacitor increases. The value of 22uF
tantalum or 150uF aluminum covers all cases of bypassing the adjustment terminal. Without
bypassing the adjustment terminal smaller capacitors can be used with equally good results.
To ensure good transient response with heavy load current changes capacitor values on the
order of 100uF are used in the output of many regulators. To further improve stability and transient
response of these devices larger values of output capacitor can be used.

PROTECTION DIODES
Unlike older regulators, the LM1085 family does not need any
protection diodies between the adjustment pin and the output
and from the output tu the input to prevent over-stressing the die.
LM1085
Internal resistors are limiting the internal current paths on the
LM1085 adjustment pin, therfore even with capacitors on the
adjustment pin no protection diode is needed to ensure device
safety under short-circuit conditions.

Diodes between the input and output are not usually needed.
Microsecond surge currents of 50A to 100A can be handled by the internal diode between the
input and output pins of the device. In norminal operations it is difficult to get those values of
surge currents even with the use of large output capacitances. If high value output capacitors are
used, such as 1000uF to 5000uF and the input pin is instantaneously shorted to ground, damage
can occur. Adiode from output to input is recommended, when a crowbar circuit at the input of the
LM1085 is used. Normal power supply cycling or even plugging and unplugging in the system will
not generate current large enough to do any damage.

The adjustment pin can be driven on a transient basis ±25V, with respect to the output without
any device degradation. As with any IC regulator, none the protection circuitry will be functional and
the internal transistors will break diwn if the maximum inout to output voltage differential is exceeded

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

RIPPLE REJECTION

The ripple rejection values are measured with the adjustment pin bypassed. The impedance of the
adjust pin capacitor at the ripple frequency should be less than the value of R1 (normally 100Ω
to 120Ω) for a proper bypassing and ripple rejection approaching the values shown. The size of
the required adjust pin capacitor is a function of the input ripple frequency. If R1=100Ω at 120Hz
the adjust pin capacitor should be 25uF. At 100kHz only 0.22uF is needed.

The ripple rejection will be a function of output voltage, in circuits without an adjust pin bypass
capacitor. The output ripple will increase directly as a ratio of the output voltage to the reference
voltage (Vout/Vref)

OUTPUT VOLTAGE

The LM1085 series develops a 1.25V reference voltage

LM1085 between the output and the adjust terminal. Placing a
resistor between these two terminals causes a constant
current to flow through R1 and down throuth R2 to set the
overall output voltage.

This current is normally the specified minium load current

of 10mA. Because IADJ is very small and constant it
represents a small error and it can usually be ignored.

LOAD REGULATION

True remote sheet specification it is not possible to

provide, because the LM1085 is a three terminal device.
LM1085
The resistance of the wire connecting the regulator to the
load will limit the load regulation.
The data sheet specification for load regulation is measured
at the bottom of the package. Negative side sensing is a
true Kelvin connection, with the bottom of the output divider
returned to the negative side of the load.
The best load regulation is obtained when the top of the
resistor divider R1 is connected directly to the case not to
the load. If R1 were connected to the load, the effective
resistance between the regulator and the load would be:
[RPX(R2+R1)]/R1 , RP = Parasitic Line Resistance
Connected as shown Fig.3 RP is not multiplied by the divider ratio. Using 16-gauge wire the
parasitic line resistance is about 0.004Ω per foot, transllating to 4mV/ft at 1A load current.

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3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed) LM1085

THERMAL CONSIDERATIONS

The LM1085 series have internal power and thermal limiting circuitry designed to protect the device
under overload cinditions. However maximum junction temperature ratings should not be exceeded
under continous normal load conditions.
Careful consideration must be given to all sourses of thermal resistance from junction to ambient,
including junction-to- ase, case-to-heat sink interface and heat sink resistance itself. To ensure
safe operating temperatures and reflect more accurately the device temperature, new thermal
resistance specifications have been developed. Unlike order reguators with a single junction-to-
case thermal resistance speccification, the data section for these new regulators provides a
separate thermal resistance and maximum juntion temperature for both the Control Section and the
Power Transistor. Calculations for both temperatures under certain conditions of ambient
temperature and heat sink resistance and to ensure that both thermal limits are met.

Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case
directly below the die. This is the lowest resistance path for the heat flow. In order to ensure the
best possible thermal flow from this area of the package to the heat sink proper mounting is
required. Thermal compound at the case-to-heat sink interface is recommended. A thermarlly
conductive spacer can be used, if the case of the device must be electrically isolated, but its
added contribution to thermal resistance has to be considered.

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