LD5535E1/A1

10/05/2017

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5535E1/A1-DS-00 October 2017

OVP events. The counter has been 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

OTP Pin

– Auto Recovery

The OTP circuit is implemented to sense whether there is

any hot-spot of power circuit like power MOSFET or

output rectifier. Once an over-temperature condition is

detected, the OTP is enabled to shut down the controller

to protect the controller. Typically, a NTC is recommended

to connect with OTP pin. The NTC resistance will

decrease as the device or ambient in high temperature.

The relationship is as below.

NTC

OTP

R

A

μ

100

V





When the VOTP is lower than the defined voltage threshold

(typ. 0.95V), the LD5535E1/A1 is going to shut down gate

output. Restarting LD5535E1/A1 successfully has to cool

down the circuit so that NTC resistance will increase and

raise VOTP up above 1.05V.

Secondary Diode Short Protection (SDSP)

–

Auto Recovery

The method that the LD5535E1/A1 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. 19.

Fig. 19

Fault Protection

There are several critical protections integrated in the

LD5535E1/A1 to prevent from damage to the power

supply. Those damages usually come from open or short

conditions on the pins of LD5535E1/A1.

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

Comp

CS

1.2V

4 cycle