ADJ

Q24

R26

0.03

R25

3

R24

160

R22

160

R23

18 k

R20

13 k

R21

400

R18

130

R19

370

R16

6.7 k

R17

12 k

Q25

Q26

Q21

Q20

Q18

Q16

C3

5 pF

R14

12 k

R15

2.4 k

Q21

D2

6.3 V

D3

6.3 V

Q19

Q17

Q15

Q14

Q13

Q12

Q11

Q9

Q7

Q5

Q3

R13

5.1 k

R12

72

R11

5.8 k

R10

4.1 k

R9

180

R7

130

R27

4 k

R8

12.4 k

6 V

Q10

Q8

Q4

Q1

Q2

R1

310

R2

310

R3

190

R4

82

R5

5.6 k

R6

200 k

Q6

C1

30 pF

C2

30 pF

Q27

D1

6.3 V

Copyright © 2017, Texas Instruments Incorporated

10

LM138QML

SNVSAA9 – OCTOBER 2017

www.ti.com

Product Folder Links: LM138QML

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Copyright © 2017, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LM138QML device is an adjustable, three-terminal, positive-voltage regulator capable of supplying more

than 5 A over an output-voltage range of 1.2 V to 32 V. It requires only two external resistors to set the output

voltage. The LM138QML device features a typical line regulation of 0.005% and typical load regulation of 0.1%. It

includes time-dependent current limiting, thermal overload protection, and safe operating area protection.

Overload protection remains functional even if the ADJUST terminal is disconnected.

The LM138QML devices are versatile in their applications, including uses in programmable output regulation and

local on-card regulation. Or, by connecting a fixed resistor between the ADJUST and OUTPUT terminals, the

LM138QML device can function as a precision current regulator. An optional output capacitor can be added to

improve transient response. The ADJUST terminal can be bypassed to achieve very high ripple-rejection ratios,

which are difficult to achieve with standard three-terminal regulators.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 NPN Darlington Output Drive

NPN Darlington output topology provides naturally low output impedance and an output capacitor is optional. To

7.3.2 Overload Block

Overcurrent and overtemperature shutdown protects the device against overload or damage from operating in

excessive heat.

7.3.3 Programmable Feedback

An op amp with 1.25-V offset input at the ADJUST terminal provides easy output voltage or current, but not both,

voltage.