SCI7631MAA 查看數據表（PDF） - Seiko Epson Corp

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SCI7631MAA

POWER SUPPLY IC - DC/DC Switching Regulators

Seiko Epson Corp 

SCI7630 Series

FUNCTIONAL DESCRIPTION

Basic Voltage Booster Operation

TR1 switches ON and OFF at the frequency of the clock

pulses from the crystal oscillator. When the transistor is

ON, the circuit stores energy in L. When it is OFF, this

energy flows through D to charge C.

L

D

VI1

VO

Tr1

C

GND

GND

The output voltage regulator regulates the boosted out-

put voltage. This voltage is determined by the level at

point A between the two resistors connecting VO and

GND. These series use an on-chip resistor to set the

output at a specified voltage.

Crystal

Reference

voltage

CD

generator

CG

Output

voltage regulator

VI1

Internal Circuits

Crystal oscillator

The SCI7633 series incorporate a crystal oscillator cir-

cuit. An external crystal and drain resistor are used to

generate the booster circuit clock. The crystal oscillator

is connected to CI and CO as shown in the following

figure.

CI

Crystal

oscillator

+

–

VSW

VO

A

GND

Crystal

RD

CG

CD

SCI7633

CO

Note

In step-up voltage operation, the ripple voltage created

by the switching operation is large relative to the output

voltage described above. This ripple voltage is affected

by external components and load conditions. The user

is advised to check this voltage carefully.

In the SCI7633 series, the crystal oscillator output is

sent to CLO as the VO system signal. The crystal oscil-

lator circuit is activated by VI but, because the output

level is shifted and the output is connected to CLO, the

oscillator output cannot be obtained without a voltage at

VO. Since the crystal oscillator is activated when an

input voltage is applied, oscillation continues even in

standby mode.

Reference voltage generator and output

voltage regulator

The reference voltage generator regulates VI1 to gener-

ate a voltage for the voltage regulator circuit.

Standby mode

Connecting PS to GND places the chip in standby

mode. In this mode, the crystal oscillator is disabled,

switching off the inductor drive transistor and the volt-

age booster circuit. Typically, PS is connected to RST.

If standby mode is not required, leave PS open as it has

a pull-up resistor.

Output voltage response compensation

The SCI7634 series incorporates a response compensa-

tion input. A response compensation capacitor is con-

nected between VCONT and VO, allowing the ripple

voltage generated by the boosted output voltage to be

suppressed to a minimum.

4–26

EPSON

SCI7000 Series

Technical Manual

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