LD5523M1

04/12/2021

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5523M1-DS-00 April 2021

IFB

IOCP

105µA

300µA

78.75µA

225µA

COMP

IOCP

0.55V

1.4V

IFB×K

VCC

UVLO(ON)

PDR

t

t

COMP

OPP

3V

t

OUT

OPP delay time

Switching

Non-Switching

OPP trip Level

Latch Released

t

AC input Voltage

AC Off

AC On( Recycle)

Switching

Fig. 17

Over Current Protection (OCP)

– Latch

When the switching current is higher than the OCP

threshold, the internal counter counts down. When the

total accumulated counting time is more than 225ms, the

controller triggers the OCP. This protection is latch

protection.

Adjustable Over Current Compensation on

FB Pin

For compensating the differential input current from

high/low line conditions on current sensing resistor,

LD5523M1 mirrors compensation current IOCP from IFB to

CS pin. The relationship of compensation current IOCP and

IFB is expressed by following equation and shown in Fig.

18.

FB

OCP

I

K

I





, where

5

7

.

0

K



K is the mirror current ratio of FB pin, and the IOCP follows

the input voltage. When the VCOMP ramps up to the IOCP

threshold 0.55V, the compensation current is added

gradually. The maximum value of IOCP is generated as

VCOMP is higher than 1.4V. The corresponding VCOMP and

IOCP are shown in Fig. 19.

The compensation current IOCP supplies an offset

voltage by external resistor ROCP, which is series

between the current sensing resistor RS and CS pin. By

selecting a proper value of the resistor ROCP in series

with the CS pin, the amount of compensation can be

adjusted.

Fig. 18

Fig. 19

Over Voltage Protection on FB Pin (FB OVP)

– Latch

An output overvoltage protection is implemented in the

LD5523M1. The auxiliary winding voltage can be reflected

from secondary winding, in which the FB pin voltage is

proportional to output voltage during the gate off time.

OVP is worked by sensing the auxiliary voltage via the

divided resistors R2, refereeing to Fig. 20. The equation of

FB OVP is shown as follows.

R2 =

R1 ∙ VFB_OVP

Va − VFB_OVP