LP38853_15 datasheet(11/30 Pages) TI1

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GND

OUT

BIAS

Undervoltage

Lockout

Thermal

Shutdown

1.2 V

Enable

VREF

0.5 V

ILIMIT

ADJ

rSS

rEN

LP38853

www.ti.com

SNVS335E – DECEMBER 2006 – REVISED NOVEMBER 2015

7 Detailed Description

7.1 Overview

The LP38853 is a high-current, low-dropout, fast-response linear regulator capable of sourcing a 3-A load with

only 240-mV dropout. This device operates from two input voltages: VBIAS provides voltage to internal circuit,

while VIN is the input voltage supplying power to load. The use of an external bias rail allows the part to operate

from ultra low VIN voltages. The fast transient response of this device makes it suitable for powering DSP,

microcontroller cores, and post regulators.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Undervoltage Lockout (UVLO)

The bias voltage is monitored by a circuit which prevents the device from functioning when the bias voltage is

below the UVLO threshold of approximately 2.45 V.

As the bias voltage rises above the UVLO threshold the device control circuitry becomes active. There is

approximately 150 mV of hysteresis built into the UVLO threshold to provide noise immunity.

When the bias voltage is between the UVLO threshold and the minimum operating rating value of 3 V the device

is functional, but the operating parameters are not be within the specified limits.

7.3.2 Supply Sequencing

There is no requirement for the order that VIN or VBIAS are applied or removed.

One practical limitation is that the soft-start circuit starts charging CSS when both VBIAS rises above the UVLO

threshold and the EN pin is above the VEN(ON) threshold. If the application of VIN is delayed beyond this point the

benefits of soft start are compromised.

In any case, the output voltage cannot be ensured until both VIN and VBIAS are within the range of specified

operating values.

If used in a dual-supply system where the regulator output load is returned to a negative supply, the output pin

must be diode clamped to ground. A Schottky diode is recommended for this diode clamp.

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