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Inrush Current Limiting Circuit for Low Dropout Regulator

IP.com Disclosure Number: IPCOM000239463D
Publication Date: 2014-Nov-10
Document File: 3 page(s) / 157K

Publishing Venue

The IP.com Prior Art Database

Abstract

In conventional low dropout regulator in-rush current during regulator output ramp-up is usually large and determined by the maximum drive capacity of the pass transistor. We propose a circuit that reduces the in-rush current in low dropout regulators. This circuit can be used for limiting driver current during power supply ramp up or while the circuit is coming out of power down.

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Inrush Current Limiting Circuit for Low Dropout Regulator

Abstract

In conventional low dropout regulator in-rush current during regulator output ramp-up is usually large and determined by the maximum drive capacity of the pass transistor.  We propose a circuit that reduces the in-rush current in low dropout regulators.  This circuit can be used for limiting driver current during power supply ramp up or while the circuit is coming out of power down.

Introduction

          In this paper we presenta technique to limit the swing across the pass transistor of a low dropout regulator during startup, which limits the in-rush current.

Functional Description

A voltage limiting circuit ensures that the voltage at the driver gate does not go below a pre-determined voltage threshold.  During the normal mode of operation, it ensures that the voltage limit circuit is turned off.

Circuit Implementation

Voltage regulator -  The LDO circuit discussed is a NMOS input error amplifier followed by a common  source driver stage.

Voltage limit circuit -  It is a NMOS transistor with its gate connected to a reference voltage Vref.  The NMOS transistor can be zero vt or any other NMOS that has the required voltage rating.

Reference voltage generation (VREF):  The reference voltage can be

-           a fixed reference voltage ( bandgap voltage)

-           Voltage generated form a voltage divider circuit between supply and ground.

-           A reference voltage that follows both supply and Vt of the drive...