SC1406

© 1999 SEMTECH CORP.

652 MITCHELL ROAD

NEWBURY PARK CA 91320

PORTABLE PENTIUM

POWER SUPPLY CONTROLLER

PRELIMINARY - August 27, 1999

10

Pentium is a registered trademark of Intel Corporation

Core Converter Soft Start Timer

The main purpose of this block is to control the ramp-

up time of the core voltage in order to reduce the ini-

tial inrush current on the core input voltage (battery)

rail. The soft start circuit consists of an internal cur-

rent source, external soft start timing capacitor, inter-

nal switch across the capacitor, and a comparator

monitoring the capacitor voltage.

LINEAR REGULATOR CONTROLLER

1.5V Linear Regulator

This block is a linear regulator controller, which drives

an external PNP bipolar transistor as a pass element.

The linear regulator is capable of delivering 500mA

steady state DC current and should support transient

current of 1A, assuming the output filtering capacitor

is properly selected to provide enough charge for the

duration of the load transient.

2.5V Linear Regulator

This block is a low drop-out (LDO) linear regulator

controller, which drives an external PNP bipolar tran-

sistor as a pass element. The LDO linear regulator is

capable of delivering 100mA steady DC current and

should support transient current of 100mA, assuming

the output filtering capacitor is properly selected to

provide enough charge for the duration of the load

transient.

Linear Regulator Soft Start Timer

A soft start timer circuit of the linear regulators is simi-

lar to that of the core converter, and is used to control

the ramp up time of the linear regulator output volt-

ages. For maximum flexibility in controlling the start

up sequence, the soft start function of the linear regu-

lators is separated from that of the core converter.

VOLTAGE CLAMP

The level translator converts an input voltage swing

on the IO rail, into a voltage swing on the CLK or VCC

rail depending on where the open drain output of the

translator is tied to through an external pull-up resistor.

The level translator has to track the input in phase,

and must be able to switch in 5ns (typical) following an

input threshold intercept.

APPLICATION INFORMATION

Power on/off Sequence