LD5537G1

07/04/2018

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5537G1-DS-00 July 2018

1.05V

t

Vcc

t

OUT

Switching

Non-Switching

t

VBNO

t

Line Voltage

0.95V

Non-

Switching

Normal Range

UVLO(on)

UVLO(off)

added to prevent incorrect OVP detection which might

occur during ESD or lightning events. However, when

typically 8 cycles of subsequent OVP events are detected,

the OVP circuit switches the power MOSFET off. As the

protection is latch, the converter restarts after the AC is

plug out and in.

ROCP

RS

CS

AUX

0.31V

OUT

Sample

Delay

Debouce

8 cycle

OVP

Fig. 17

Delay

Sample

Out

AUX Winding

CS/OVP

Fig. 18

Brown-out Protection (BNO)

The LD5537G1 is programmable to set the brownout

protection point though BNO pin. The voltage across the

BNO pin is proportional to bridge rectifier of AC input.

A

brownout comparator is implemented to detect the

abnormal line condition. As soon as the condition is

detected, it will shut down the controller to prevent the

damage. Fig. 19 shows the operation. When VBNO falls

below 0.95V, the gate output will remain off even VCC has

already achieved UVLO(ON). It therefore makes VCC

hiccup between UVLO(ON) and UVLO(OFF). Unless the

line voltage is enough to pull VBNO larger than 1.05V, the

gate output will not start switching even when the next

UVLO(ON) is tripped. A hysteresis is implemented to

prevent the false trigger during turn-on and turn-off.

Fig. 19

Fault Protection

There are several critical protections integrated in the

LD5537G1 to prevent from damage to the power supply.

Those damages usually come from open or short

conditions on the pins of LD5537G1.

In case under such conditions listed below, the gate

output will turn off immediately to protect the power circuit.

1.

CS pin floating

2.

COMP pin floating