LD5523K

05/16/2018

11

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5523K-DS-00 May 2018

CS

VCC

GND

LD5523K

Can be removed if the negative

spike is not over spec. (-0.3V).

OUT

275ns

blanking

time

Fig. 13

CS

VCC

GND

LD5523K

RC filter is needed whenever the negative

spike is exceed - 0.3 V or the total spike

width is over 275 nS LEB period.

OUT

Fig. 14

Output Stage and Maximum Duty

An output stage of a CMOS buffer, with typical 350mA

driving capability, is incorporated to drive a power

MOSFET directly. The maximum duty of LD5523K is

limited to 81% avoid detecting QR fail.

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 LD5523K 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

The VGS ratings of the nowadays power MOSFETs are

often limited up to max. 28V. To prevent the VGS from the

fault condition, LD5523K is implemented with an OVP

function on VCC. Whenever the VCC voltage is higher

than the OVP threshold voltage, the output gate drive

circuit will be shutdown simultaneously thus to stop the

switching of the power MOSFET until the next UVLO(ON).

The VCC OVP function in LD5523K 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.

VCC

UVLO(on)

UVLO(off)

t

OVP Tripped

t

OUT

Switching

Switching

Non-Switching

OVP Level

Fig. 15