LD5523T

04/08/2021

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5523T-DS-00 April 2021

Under Voltage Protection 2 on FB Pin (FB

UVP 2) – Auto Recovery

To protect the circuit from damage due to output under

voltage condition, LD5523T is implemented with an UVP

function on FB pin. The output voltage is detected by PD

controller, if output voltage falls to PD UVP level in

abnormal condition, PD controller will control output

voltage to drop immediately. The FB pin voltage is

proportional to output voltage during the gate off time.

Therefore, as VFB is lower than FB UVP trip level during

gate off region over 6 cycles, then the FB UVP 2 will be

activated to stop the switching of the power MOSFET

until the next UVLO(on). The Fig. 19 shows its

operation.

Fig. 19

Output Short Circuit Protection (OSCP) –

Auto Recovery

The OSCP function can prevent the damage from

output short circuit. Once the output is shorted, Vo and

VCC drop immediately. According to the close loop

control, COMP voltage will pull high in the meanwhile.

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.

Therefore, VFB also drops during gate off region. At this

time, the OSCP protection will be triggered and turn off

the gate driving.

Oscillator and Switching Frequency

The LD5523T is implemented with frequency swapping

function which helps the power supply designers to both

optimize EMI performance and lower system cost.

Green Mode Operation

By using the green-mode control, the switching

frequency can be reduced under the light load condition.

This feature helps to improve the efficiency in light load

conditions. The green-mode control is Leadtrend

Technology’s own property.

Fault Protection

There are several critical protections integrated in the

LD5523T to prevent from damage to the power supply.

Those damages usually come from open or short

conditions on the pins of LD5523T.

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