MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

16/41

3.4.4 VCC-GND short circuit protection

If Vcc and GND short-circuit, current flows continuously to the startup circuit, and heat builds up in the IC.

A function reduces Icc in the event of short circuits to prevent excessive heat buildup.

3.4.5 Leading edge blank (LEB)

The MS1003SH and MS1004SH incorporate a leading edge blank function, which rejects trigger signals

from the drain current detection circuit for a certain period of time after the main switching device is turned

on to improve the noise margin.

This function prevents false detection due to a gate drive current generated the moment the main switching

device is turned on or to a current discharged from the resonating capacitor.

3.4.6 On-trigger malfunction prevention circuit

At startup or in the event of a load short circuit, the output

voltage drops to levels significantly below the set voltage.

Since the control coil voltage is proportional to the output

voltage, it drops significantly as well. In this case, a false

on-trigger timing may be detected due to the ringing voltage

while the device is off. The device may switch before the

current critical point.

To address this problem, the MS1003SH and MS1004SH

incorporate a circuit for preventing on-trigger malfunctions at

startup or in the event of short circuits.

This function disables the on-trigger during the period Tondead after the main switching device in the IC is

turned off. This prevents false detection due to the ringing voltage while the device is off.

3.4.7 TSD

The MS1003SH and MS1004SH incorporate a thermal shutdown circuit. The IC is latched at 150°C (TYP),

and oscillation is stopped. The IC is unlatched by momentarily dropping the VCC pin voltage to the VUL

(unlatch voltage) or below.

オントリガ禁止期間

2次整流ダイオード電流

約0.25V

Output current Io

Main SW device

Control voltage

Vcc

Feedback voltage

VF/B

The bias assist function turns off after the IC is latched.

Overload beyond the droop setting

The on-trigger is disabled

during this period.

Approx.

0.25 V

Secondary rectification diode current

Tondead