LM338T Reference Tables, Pins & Specifications

Pin reference

Signal names, electrical functions and connection guidance

TO-220

Physical pin numbers3 pins

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LM338T pin functions and connections
Signal	Type	Function & connection
ADJUST	Floating reference terminal	The feedback loop holds OUTPUT approximately 1.24 V above ADJUST. Connection guidance Connect the junction of R1 from OUTPUT and R2 to the return. This is not ground; adjustment-pin current contributes IADJ × R2 to output voltage.
OUTPUT	Regulated output and tab	Supplies the external load and feedback divider. The metal tab is electrically connected to OUTPUT. Connection guidance Connect R1 close to this lead and return R2 near the load return. A grounded heatsink needs appropriate electrical insulation from the live output tab.
INPUT	Unregulated input	Powers the series pass stage. Connection guidance Use +9 V in the example, with a local 0.1 µF bypass to the common return. Recommended input-to-output differential is 3–40 V; electrical reference tests use 3–35 V. Allow margin from the 40 V absolute differential limit.

Operating reference

LM338 · TI SNVS771D

Manufacturer-referenced values8 parameters

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Parameter	Value	Conditions / notes
Nominal adjustable output	1.2–32 V	Subject to headroom, load and thermal limits
Operating junction	0–125°C	LM338 rating; not ambient temperature
Reference voltage min / typ / max	1.19 / 1.24 / 1.29 V	3–35 V differential; 10 mA–5 A; 0–125°C
Adjustment current	45 µA typical; 100 µA maximum	Flows out of ADJUST
Adjustment current change	0.2 µA typical; 5 µA maximum	10 mA–5 A; 3–35 V differential
Recommended differential	3–40 V	Allow design margin; reference accuracy tests use 3–35 V
Absolute differential range	−0.3 to +40 V	Stress rating; not a regulation guarantee
Storage temperature	−65 to +150°C	Unpowered storage

Electrical limits apply under the manufacturer power and test conditions. Individual maxima cannot be combined.

Regulation and rejection

Values at constant junction temperature

Manufacturer-referenced values8 parameters

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Parameter	Value	Conditions / notes
Line regulation, 25°C	0.005 typical / 0.03 max. %/V	3–35 V differential
Line regulation, 0–125°C	0.02 typical / 0.06 max. %/V	Same differential range
Load regulation, 25°C	0.1 typical / 0.5 max. %	10 mA–5 A
Load regulation, 0–125°C	0.3 typical / 1 max. %	10 mA–5 A
Thermal regulation	0.002 typical / 0.02 max. %/W	20 ms pulse
Ripple rejection, no CADJ	60 dB typical	10 V output; 120 Hz
Ripple rejection, 10 µF CADJ	60 dB minimum; 75 dB typical	10 V output; 120 Hz
Output noise	0.003% RMS typical	10 Hz–10 kHz; percentage of output

The manufacturer load-regulation and temperature-stability rows omit printed percent unit symbols; these values are percentages as defined by the regulation parameters. Typical values are not guarantees.

Load and time-dependent limiting

Specified conditions matter

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Minimum load	3.5 mA typical; 10 mA maximum required	35 V differential; 0–125°C
DC current limit	5 A minimum; 8 A typical	Differential ≤10 V; thermal/power restrictions
0.5 ms peak limit	7 A minimum; 12 A typical	Differential ≤10 V; not continuous output
Limit at 30 V differential	1 A typical	No minimum listed in the LM338 row
Example divider current	1.24 / 110 ≈11.27 mA	Nominal reference
Worst-case divider minimum	1.19 / 111.1 ≈10.71 mA	110 Ω at +1%; exceeds 10 mA requirement

Electrical specifications are limited to 25 W for TO-220 up to 15 V differential; above that internal protection imposes additional limits. This is not a no-heatsink power rating.

TO-220 thermal reference

NDE package · source test-board metrics

Manufacturer-referenced values8 parameters

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Parameter	Value	Conditions / notes
RθJA	22.9°C/W	Junction-to-ambient; standardized source conditions
RθJC(top)	15.7°C/W	Junction to package top
RθJC(bot)	0.7°C/W	Junction to bottom case / metal heat path
RθJB	4.1°C/W	Junction-to-board
ψJT / ψJB	2.1 / 4.1°C/W	Characterization parameters, not thermal resistances
Metal tab	Electrically OUTPUT	Insulate from a grounded heatsink as required
Example pass-stage loss	≈0.446 W	(9−4.96) × (4.96/50 + 1.24/110)
5 A with a 4 V drop	Approximately 20 W	Requires a designed thermal path and safe-area check

Do not apply the tab thermal path to the plastic top or use board θJA as a universal heatsink figure. Estimate junction temperature for the actual mounting.

Bypass and discharge paths

Manufacturer application guidance

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Input bypass	0.1 µF disc or 1 µF solid tantalum	Near INPUT and common return
Output capacitor	1 µF solid tantalum or 25 µF aluminum	Improves transient response; optional in suitable circuits
Small output capacitance	500–5000 pF may ring	See source stability guidance
Adjustment bypass	10 µF for improved ripple rejection	Optional; omitted in this example
Output discharge diode	No diode needed in stated ≤100 µF, ≤15 V case	Source section 7.2.1.2.3; evaluate externally driven rails separately
Adjustment discharge diode	No protection needed in stated ≤10 µF, ≤25 V case	Review larger stored charge and short-circuit paths

This example has 1 µF output capacitance near 5 V and no ADJ bypass; follow the manufacturer protection topology when conditions change.

Nominal near-5 V supply

9 V input · calculated example

Manufacturer-referenced values7 parameters

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Parameter	Value	Conditions / notes
R1 / R2	110 Ω / 330 Ω, 1%	OUT-to-ADJ / ADJ-to-GND
Output before IADJ	1.24 × (1+330/110) = 4.96 V	Uses typical reference
Typical IADJ contribution	45 µA × 330 Ω = 14.85 mV	Output becomes about 4.97485 V
50 Ω load	99.2 mA; 0.492 W at 4.96 V	Use at least a 1 W resistor
Total nominal output current	110.47 mA	Load plus divider; ignores small IADJ correction
Pass-stage dissipation	About 0.446 W	Nominal 9 V input
Reference/resistor bounds before IADJ	4.689–5.238 V	1.19–1.29 V reference and independent 1% divider extremes

Illustrative calculations, not a running circuit measurement. Check actual output and heating.

Physical pins and package

LM338T/NOPB · TO-220

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Front-view lead order	1 ADJUST · 2 OUTPUT · 3 INPUT	Marking toward you, leads down
Tab	OUTPUT	Not ground
Lead pitch	2.54 mm nominal	TI NDE0003B
Footprint	1.30 mm finished holes; 2.00 mm pads	Original TEP vertical starting footprint
Other family package	LM338K metal TO-CAN	Different pin layout; not the selected footprint
SMD option	No SMD package verified in this TI sheet	No unrelated substitute is presented

Confirm the ordered part, actual lead forming, fabrication clearance and heatsink space.