XC9301/9302

Series

602

6

■Operational Explanation

Ramp Wave

OSC

Error Amp.

Comparator

Buffer,

Driver

PWM/PFM

Controller

Compensation

CE

Vref with

Soft Start,

+

-

+

-

Generator,

PWM

Phase

CE

GND

EXT/

＜Block Diagram＞

CE

SD1

L

SD2

PSW

NSW

GND

EXT

CE

＜Circuit Connection Example＞

The XC9301/9302 series are PWM (PWM/PFM switching) step-up/down DC/DC converter controller ICs. The XC9302 series switches to PFM

operations during light loads and is very efficient over a wide range in relation to load. Further, the efficiency can be maintained over a wide

input voltage range as both step-up & step-down operations are PWM controlled. Output voltage settings are laser trimmed.

[ON TIME]

[OFF TIME]

stored at L.

■Block Diagram Explanation

<Error Amp.>

The error amplifier is used as an output voltage monitor. It compares the reference voltage with the feedback from the voltage divided by the

internal resistor. Should a voltage higher than the reference voltage be fedback, the output of the error amp will increase.

<PWM Comparator>

The PWM comparator compares the output of the error amp with the ramp wave. When the voltage at the output of the error amp is low, the

EXT/ pin will be LOW level (Switching ON time).

<Ramp Wave Generator>

The ramp wave generator, as the name suggests, generates the switching frequency's ramp wave.

<PWM / PFM Controller>

With the XC9302 series, control is automatically switched between PWM and PFM according to the size of the load.

<Vref with Soft Start, CE>

The start up of the Vref voltage at the error amp's input is gradual due to the internal capacitor and low current circuit. Because of this soft-start

function, the operations of the error amp's 2 inputs are balanced and the EXT/ pin's ON time can be manipulated to produce longer ON times.

Further, with the UVLO function, the signal will be such so as not to turn the MOS switch ON until any instability in the internal circuit stabilizes

during soft-start time. Even in cases where input voltage is so low as to produce instability in the IC, the UVLO function will operate and the

MOS switch will be turned OFF.

06S_15XC9301/02新規 02.9.12 3:28 PM ページ 602