LD5523T

04/08/2021

11

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5523T-DS-00 April 2021

Fig. 13

Fig. 14

CCM Switching Frequency Clamp

According to the QR operation principle, the switching

frequency is inversely proportional to the output power.

Therefore, as the output power increases, the switching

frequency can become rather low without limiting. The

CCM switching frequency of LD5523T is clamped at 65

kHz internally to provide the optimized operations by

considering the EMI performance, thermal treatment,

component sizes and transformer design

.

Over Voltage Protection on VCC Pin (VCC

OVP) – Auto Recovery

LD5523T is implemented with an OVP function on VCC.

Whenever the VCC voltage is higher than the OVP

threshold voltage, the LD5523T will be shutdown

simultaneously thus to stop the switching of the power

MOSFET until the next UVLO(ON).The VCC OVP

function in LD5523T is an auto-recovery type protection.

The Fig. 15 shows its operation.

On the other hand, if the OVP condition is removed, the

VCC level will get back to normal level and the output

will automatically return to the normal operation.

Fig. 15

Over Load Protection (OLP) – Auto

Recovery

To protect the circuit from damage due to over-load

condition and short or open-loop condition, the LD5523T

is implemented with smart OLP function. It also features

auto –recovery function, see Fig. 16 for the waveform. In

case of fault condition, the feedback system will force

the voltage loop toward the saturation and then pull the

voltage high on COMP pin (VCOMP). When the VCOMP

ramps up to the OLP threshold of 2.8V and continues

over OLP delay time, the protection will be activated and