UPC1935 datasheet(17/28 Pages) NEC

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Data Sheet G13418EJ3V0DS00

µµµµ PC1935

3.5

ON/OFF Control

3.5.1

Channel 1 (for step-up)

The ON/OFF signal control method of the output oscillation of channel 1 is to input the ON/OFF signal from ON1 as

shown in Figure 3-3. For channel 1, 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 3-3 ON/OFF Control (channel 1 for step-up)

(1) When ON1 is high: OFF status

Q11: ON

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

D11: ON

→ II1 pin: High level → FB1 output: Low level

(2) When ON1 is low: ON status (start up)

Q11: OFF

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

D11: OFF

→ II1 pin: Low level → FB1 output: High level

(3) When ON1 goes high again after start up (SW: OFF): OFF status

Q11: ON

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

D11: ON

→ II1 pin: High level → FB1 output: Low level → PWM comparator output duty: 0 %

→ Converter output voltage (VO1) drops.

Caution Even if start up is executed by making ON1 low again after (3), soft start is not executed because the

soft start select switch (SW) remains OFF. To execute soft start of channel 1 again, drop VCC to 0 V

once.

–

VO1

D11

ON1

Q11

PWM comparator

SCP comparator

(common to each channel)

CDLY

DLY

R12

FB1

VREF

R11

II1

0.3 V

0.63 V

Error amplifier

To output stage

Oscillation section

(common to each channel)

Dead time

setting: 85 %

(internally fixed)

(Converter

output

voltage)

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