+

Current

Limit

Thermal

Shutdown

IN

OUT

GND

Bandgap

Reference

OVSD

(§30 V)

PNP

LM2940-N, LM2940C

www.ti.com

SNVS769J – MARCH 2000 – REVISED DECEMBER 2014

7 Detailed Description

7.1 Overview

The LM2940 positive voltage regulator features the ability to source 1 A of output current with a dropout voltage

of typically 0.5 V and a maximum of 1 V over the entire temperature range. Furthermore, a quiescent current

reduction circuit has been included which reduces the ground current when the differential between the input

voltage and the output voltage exceeds approximately 3 V. The quiescent current with 1 A of output current and

an input-output differential of 5 V is therefore only 30 mA. Higher quiescent currents only exist when the regulator

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Short-Circuit Current Limit

The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The

LDO is not designed to operate in a steady-state current limit. During a current-limit event, the LDO sources

constant current. Therefore, the output voltage falls when load impedance decreases. Note, also, that if a current

limit occurs and the resulting output voltage is low, excessive power may be dissipated across the LDO, resulting

a thermal shutdown of the output.

7.3.2 Overvoltage Shutdown (OVSD)

Input voltage greater than typically 30 V will cause the LM2940 output to be disabled. When operating with the

input voltage greater than the maximum recommended input voltage of 26 V, the device performance is not

ensured. Continuous operation with the input voltage greater than the maximum recommended input voltage is

discouraged.

7.3.3 Thermal Shutdown (TSD)

The LM2940 contains the thermal shutdown circuitry to turn off the output when excessive heat is dissipated in

the LDO. The internal protection circuitry of the LM2940 is designed to protect against thermal overload

conditions. The TSD circuitry is not intended to replace proper heat sinking. Continuously running the device into

thermal shutdown degrades its reliability as the junction temperature will be exceeding the absolute maximum

junction temperature rating.

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Product Folder Links: LM2940-N LM2940C