LD7750 datasheet(13/20 Pages) LEADTREND

13 / 20 page

LD7750

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD7750-DS-00b February 2010

remove the AC power cord and restart AC power-on

recycling. The detailed operation is depicted in Fig. 19.

Pull-Low Resistor on the Gate Pin of

MOSFET

An anti-floating resistor is built in with the OUT pin to

prevent the output from any uncertain state. Otherwise, it

may cause the MOSFET to work abnormally or mis-trigger.

However, such design won’t cover the condition of

disconnection between the OUT pin and the gate terminal

for the MOSFET. Thus it is still strongly recommended

to have a resistor connected at the MOSFET gate

terminal (as shown in Fig. 20) to provide extra protection

for fault conditions.

This external pull-low resistor is to prevent the MOSFET

from damage during power-on when the gate resistor Rg

is disconnected. In such a fault condition, as show in Fig.

21, the resistor R8 can provide a discharge path to avoid

the MOSFET from being falsely triggered by the current

through the gate-to-drain capacitor CGD. Therefore, the

MOSFET should be always pulled-low to persist in

off-state.

UVLO(on)

UVLO(off)

AC input Voltage

OTP

OUT

Switching

Non-Switching

VCC

1.05V

0.95V

V(-)Latch

OTP Release

PDR (8V)

AC Off

AC On (Recycle)

Latch Released

Fig. 19

Fig. 20

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