Document Number: 70190

S11-0975-Rev. G, 16-May-11

www.vishay.com

9

Vishay Siliconix

Si9130

This document is subject to change without notice.

3.3 V Switching Supply

The 3.3 V supply is regulated by a current-mode PWM

controller

in

conjunction

with

several

externals:

two

N-Channel MOSFETs, a rectifier, an inductor and output

bootstrap circuit consisting of a 100 nF capacitor and diode

efficiency by reducing the voltage across the rectifier diode.

A low value sense resistor in series with the inductor sets the

maximum current limit, to disallow current overloads at

power-on or in short-circuit situations.

The

soft-start

feature

on

the

Si9130

is

capacitor

source to the external capacitor connected to GND. Excess

currents at power-on are avoided, and power-supplies can

be sequenced with different turn-on delay times by selecting

the correct capacitor value.

5 V Switching Supply

The 5 V supply is regulated by a current-mode PWM

controller which is nearly the same as the 3.3 V output. The

dropout voltage across the 5 V supply, as shown in the

schematic in Figure 1, is 400 mV (typ) at 2 A. If the voltage

at V+ falls, nearing 5 V, the 5 V supply will lower as well, until

undervoltage lockout threshold. Below this threshold, the 5 V

controller is shut off.

The frequency of both PWM controllers is set at 300 kHz

when the SYNC pin is tied to REF. Connecting SYNC to

Figure 2. Si9130 Block Diagram

+ 5 V LDO

Linear

Regulator

+ 3.3 V

Reference

ON

300 kHz/200 kHz

Oscillator

ON

3.3 V

PWM

Controller

(See Figure 3)

5 V

PWM

Controller

(See Figure 3)

STANDBY

PGND

V+

REF

SHDN

SYNC

4.5 V

4 V

2.8 V

ON

ON

3.6ADJ

3.45ADJ