MB3788 Просмотр технического описания (PDF) - Fujitsu

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производитель

MB3788

SWITCHING REGULATOR CONTROLLER

Fujitsu 

MB3788

s HOW TO SET TIME CONSTANT FOR TIMER & LATCH-TYPE SHORT-CIRCUIT

PROTECTION CIRCUIT

If the load conditions of the switching regulator are stable, the outputs of comparators 1 and 2 do not change, so the SP comparator outputs a

High level. At this time, the SCP pin (pin 15) is held at about 50 mV.

If the load conditions change suddenly due to a load short-circuit, for example, the output voltage of the comparator of the channel becomes a

High-level signal (more than 2.1 V). Then, the SVP comparator outputs a Low level and transistor Q1 is turned off. The short-circuit protection

capacitor CPE externally connected to the SCP pin starts to charge.

VPE = 50 mV + tPE × 10-6/CPE

0.65 = 50 mV + tPE × 10-6/CPE

CPE = tPE /0.6 (s)

Once the capacitor CPE is charged to about 0.65 V, the SR latch is set and the output drive transistor is turned off. At this time, the duty cycle

is made low and the output voltage of the SCP pin (pin 15) is held at Low level. This closes the SR latch input to discharge CPE.

1 µA

2.5 V

Comparator 1

Comparator 2

2.1 V

15

S

R

-

-

Q2

+

Q1

Low

input

PWM

SR latch-type

voltage comparator

CPE

circuit

protection

circuit

OUT

Fig. 5 Latch-Type Short-Circuit Protection Circuit

14

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