S1F76300 Series

FUNCTIONAL DESCRIPTIONS

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.

LD

VI1VO

Tr1 C

GND

GND

Internal Circuits

Crystal oscillator

The S1F76330 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

S1F76330

 

 

CO

 

 

RD

CG

CD

 

The output voltage regulator regulates the boosted output 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

CD

CG

 

voltage

Output

 

 

generator

 

 

voltage regulator

VI1

VSW

Crystal

oscillator

VO

A

+

–

GND

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.

S1F76300

Series

 

 

In the S1F76330 series, the crystal oscillator output is sent to CLO as the VO system signal. The crystal oscillator 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 generate 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 voltage 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 S1F76340 series incorporates a response compensation input. A response compensation capacitor is connected between VCONT and VO, allowing the ripple voltage generated by the boosted output voltage to be suppressed to a minimum.

S1F70000 Series Technical Manual

EPSON

4–27