Thermal

Limit

Soft-Start

Discharge

OUT

V

OUT

FB

PG

IN

BIAS

SS

EN

Hysteresis

and Deglitch

Current

Limit

UVLO

0.44 A

m

0.8V

Reference

0.9

V

´

REF

GND

C

SS

R

1

R

2

Copyright © 2016, Texas Instruments Incorporated

11

TPS74901

www.ti.com

SBVS082I – JUNE 2007 – REVISED MAY 2016

Product Folder Links: TPS74901

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Copyright © 2007–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The TPS74901 belongs to a family of low-dropout regulators that feature soft-start capabilities. These regulators

use a low-current bias input to power all internal control circuitry, allowing the NMOS pass transistor to regulate

very-low input and output voltages.

The use of an NMOS-pass FET offers several critical advantages for many applications. Unlike a PMOS topology

device, the output capacitor has little effect on loop stability. This architecture allows the TPS74901 to be stable

with any capacitor with a value of 2.2 µF or greater. Transient response is also superior to PMOS topologies,

The TPS74901 features a programmable voltage-controlled soft-start circuit that provides a smooth, monotonic

start-up and limits start-up inrush currents that may be caused by large capacitive loads. A power-good (PG)

output is available to allow supply monitoring and sequencing of other supplies. An enable (EN) pin with

capability allows for inexpensive, easy-to-design, and efficient linear regulation between the multiple supply

voltages often present in processor-intensive systems.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Enable and Shutdown

hysteresis and deglitching for use with relatively slowly ramping analog signals. This configuration allows the

TPS74901 to be enabled by connecting the output of another supply to the EN pin. The enable circuitry typically

signal.

The enable threshold is typically 0.8 V and varies with temperature and process variations. Temperature

variation is approximately –1 mV/°C; process variation accounts for most of the rest of the variation to the 0.4-V

and 1.1-V limits. If precise turnon timing is required, a fast rise-time signal must be used to enable the

TPS74901.