LD9535CGS datasheet(12/17 Pages) LEADTREND

12 / 17 page

LD9535C

09/21/2020

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD9535C-DS-00 September 2020

VCC

GND

LD9535C

Drain

LEB time

VBULK

Fig. 15

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 LD9535C 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

LD9535C is implemented with an OVP function on VCC.

Whenever the VCC voltage is higher than the OVP

threshold voltage, the LD9535C will be shutdown

simultaneously thus to stop the switching of the power

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

function in LD9535C is an auto-recovery type protection.

The Fig. 16 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.

VCC

UVLO(on)

UVLO(off)

OVP Tripped

OUT

Switching

Non-Switching

OVP Level

Fig. 16

Over

Load

Protection

(OLP)

– Auto

Recovery

To protect the circuit from damage due to over-load

condition

and

short

open-loop

condition,

the

LD9535C is implemented with smart OLP function. It

also features auto

–recovery function, see Fig. 17 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 then turn off the gate output to stop the

switching of power circuit.

With the protection mechanism, the average input

power will be minimized to remain the component

temperature and stress within the safe operating area.

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