Data Sheet G13690EJ3V0DS00

14

µµµµ PC1933

3.4

ON/OFF Control

The ON/OFF control method of the output oscillation is to input the ON/OFF signal from ON as shown in Figure 3-2.

Soft start or timer latch (SCP) is internally selected. Soft start is executed when the first start signal is input. When the

end of soft start is detected, the soft start select switch is turned OFF and the timer latch circuit operates.

Figure 3-2 ON/OFF Control

(1) When ON is high: OFF status

Q1: ON

→ DLY pin: Low level → Output duty of PWM comparator: 0 %

D1: ON

→ II pin: High level → FB output: Low level

(2) When ON is low: ON status (start up)

Q1: OFF

→ CDLY is charged in the sequence of [VREF → R1 → SW → DLY pin → CDLY] → Soft start

D1: OFF

→ II pin: Low level → FB output: High level

(3) When ON goes high again after start up (SW: OFF): OFF status

Q1: ON

→ DLY pin: Low level (Nothing happens because SW is OFF.)

D1: ON

→ II pin: High level → FB output: Low level → PWM comparator output duty: 0 %

→ Converter output voltage (VO) drops.

Caution Even if start up is executed by making ON low again after (3), soft start is not executed because the

soft start select switch (SW) remains OFF. To execute soft start again, drop VCC to 0 V once.

+

+

–

+

–

–

+

VO

D1

ON

Q1

Q

PWM comparator

SCP comparator

CDLY

DLY

R2

R

FB

SW

VREF

R1

II

0.3 V

0.63 V

Error amplifier

To output stage

(Converter

output

voltage)

Dead time

setting: 85 %

(internally fixed)

Oscillation section

(common to each channel)