US1050

2-35

Rev. 1.3

10/27/00

APPLICATION INFORMATION

APPLICATION INFORMATION

Introduction

The US1050 adjustable Low Dropout (LDO) regulator is

a 3 terminal device which can easily be programmed

with the addition of two external resistors to any volt-

ages within the range of 1.25 to 5.5 V.This regulator

unlike the first generation of the 3T regulators such as

LM117 that required 3V differential between the input

and the regulated output,only needs 1.3V differential to

maintain output regulation. This is a key requirement for

today’s microprocessors that need typically 3.3V sup-

ply and are often generated from the 5V supply. Another

major requirement of these microprocessors such as

the Intel P54C

from zero to several amps in tens of nanoseconds at

the processor pins ,which translates to an approximately

300 to 500 nS current step at the regulator . In addition,

the output voltage tolerances are also extremely tight

and they include the transient response as part of the

specification.For example Intel VRE

for a total of

lation and 0 to 4.6A load step.

The US1050 is specifically designed to meet the fast

current transient needs as well as providing an accurate

initial voltage , reducing the overall system cost with the

need for fewer output capacitors.

PIN DESCRIPTIONS

PIN DESCRIPTIONS

PIN #

PIN SYMBOL

PIN DESCRIPTION

1

Adj

A resistor divider from this pin to the Vout pin and ground sets the output voltage.

2

Vout

The output of the regulator. A minimum of 10uF capacitor must be connected

from this pin to ground to insure stability.

3

Vin

The input pin of the regulator. Typically a large storage capacitor is connected

from this pin to ground to insure that the input voltage does not sag below the

minimum drop out voltage during the load transient response. This pin must

always be 1.3V higher than Vout in order for the device to regulate properly.

BLOCK DIAGRAM

BLOCK DIAGRAM

Figure 1 - Simplified block diagram of the US1050

Vin 3

1050blk1-1.0

+

1 Adj

+

2 Vout

THERMAL

SHUTDOWN

CURRENT

LIMIT

1.25V