MB3883(1998) データシートの表示（PDF） - Fujitsu

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MB3883
(Rev.:1998)

6-ch DC/DC Converter IC with Synchronous Rectifier for Voltage Step-up and Step-down

Fujitsu 

MB3883

s SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT

The short detection comparator (SCP comparator) in each channel monitors the output voltage.

While the switching regulator load conditions are stable on all channels, the LOG_SCP output remains at “H”

level, transistor Q1 is turned on, and the CSCP terminal (pin 18) is held at “L” level.

If the load condition on a channel changes rapidly due to a short of the load, causing the output voltage to drop,

the output of the short detection comparator on that channel goes to “H” level. This causes transistor Q1 to be

turned off and the external short protection capacitor CSCP connected to the CSCP terminal to be charged at 1.0

µA.

Short detection time (tPE)

tPE (s) =: 0.70 × CSCP (µF)

When the capacitor CSCP is charged to the threshold voltage (VTH =: 0.70 V), the latch is set and the external

FET is turned off (dead time is set to 100%). At this point, the latch input is closed and the CSCP terminal is

held at “L” level.

A

R1

34

−IN1

R2

1.0 V

SCP

− Comp.1

+

External FET

Drive

1−1

Drive

1−2

37

OUT1−1

38

OUT1−2

0.9 V

CSCP

18

1 µA

CSCP

Q1

SCP

− Comp.6

+

LOG_SCP

bias

S

R

Timer-latch short

protection circuit

UVLO

Drive

6

bias

47

OUT6

Ref

Power

ON/OFF CTL

20

CTL

Timer-latch short circuit protection circuit

26

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