LD7523

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD7523-DS-00

June 2009

Vpin1

Line

Compensation

1.30V

52mV

160mV

gain=0.04

150mV

3.75V

Linear Region

4.0V

Turn-Off

Region

Fig. 24

Over Load Protection (OLP)

To protect the circuit from damage under over load

condition or short condition, a smart OLP function is

implemented in the LD7523. Figure 25 shows the

waveforms of the OLP operation.

In such cases, the

feedback system will force the feedback voltage loop

toward the saturation and pull the voltage of COMP pin

(VCOMP) to high.

Once the VCOMP trips the OLP

threshold of 5.0V and stays for more than 60mS, the

protection will be activated and then turns off the gate

output to stop the switching of power circuit.

The 60mS

delay time is to prevent the false trigger from the power-on

and turn-off transient.

The Fig. 26 shows the other application example. The

VCC of LD7523 will be supplied by an auxiliary source

voltage (e.g. standby power) instead. Once the voltage of

COMP pin trips the OLP threshold voltage (5.0V) and

stays for more than 60mS, OUT pin will stop switching

soon. The VCC voltage will not descend since VCC is

supplied by an auxiliary voltage source. Otherwise, the

internal OLP de-latch counter will active and count for a

skipping duration (500mS). It is called as OLP SKIP

DURATION. The OUT pin will stop switching until the OLP

de-latch counter is reset and then resume to normal

switching.

By using such protection mechanism, the average input

power can be reduced to minimum level to control the

component temperature and stress within the safety

operation area.

VCC

UVLO(on)

UVLO(off)

T

T

COMP

Over Load

5V

T

OUT

OLP Delay Time

Switching

Switching

Non-Switching

OLP Delay Time

Over Load

Switching

OLP Delatch by UVLO(off)

Fig. 25