LD5537B1/I1

12/18/2018

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5537B1/I1-DS-00 December 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)

Delay

Sample

Out

AUX Winding

CS/OVP

Fig. 18

Brown-out Protection (BNO)

The LD5537B1/I1 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.

LD5537B1/I1 can floating this pin If haven

’t need BNO

function.

Fig. 19

Secondary Diode Short Protection (SDSP)

–

Auto Recovery for LD5537B1

The method that the LD5537B1/I1 judges the logic of

SDSP is described briefly as follows. When VCS is higher

than 1.2V, it will reduce the frequency first, even the Ton <

LEB+TPD. When the count is up to 4 times, its gate will be

turned-off, shown as Fig. 20.

Fig. 20

Comp

CS

1.2V

4 cycle