LD7576GS datasheet(13/22 Pages) LEADTREND

13 / 22 page

LD7576/76H/76J/76K

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD7576-DS-04a

December 2009

VCC

UVLO(on)

UVLO(off)

COMP

OLP

5.0V

OUT

OLP Delay Time

Switching

Non-Switching

OLP trip Level

2nd UVLO(off)

OLP Counter Reset

Fig. 17

UVLO(on)

UVLO(off)

AC input Voltage

OUT

Switching

Non- Switching

VCC

5.0V

COMP

PDR(8V)

AC Off

AC On( Recycle)

Latch Released

OLP Delay Time

OLP trip Level

Fig. 18

OVP (Over Voltage Protection) on Vcc -

Auto Recovery

The maximum VGS ratings of the power MOSFETs are

mostly for 30V. To prevent the VGS enter fault condition,

LD7576X series is implemented with OVP function on Vcc.

Whenever the Vcc voltage is higher than the OVP

threshold, the output gate drive circuit will be shutdown

simultaneously and the switching of the power MOSFET

is disabled until the next UVLO(on).

The

Vcc

OVP

functions

LD7576/76J

are

auto-recoverable.

If the OVP condition, usually caused

by open-loop of feedback, is not released, the Vcc will trip

the OVP level again and re-shutdown the output.

The

Vcc works in hiccup mode as shown in Figure 19.

Otherwise, when the OVP condition is removed, the Vcc

level will be resumed and the output will automatically

return to the normal operation.

OVP (Over Voltage Protection) on Vcc -

Latch mode

Similar with the behavior for OLP latch-mode, whenever

the voltage on the Vcc pin is higher than the OVP

threshold, the output gate drive circuit will be shut down

simultaneously to latch off the switching of the power

MOSFET. As soon as the voltage on Vcc pin drops below

OVP threshold and starts AC-recycling again, it will

recover to normal operation.

Figure 20 shows its operation.

Fig. 19

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