LD5762E datasheet(13/19 Pages) LEADTREND

13 / 19 page

LD5762E/A

11/09/2017

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5762E/A-DS-00 November 2017

more than 50%. To stabilize the control loop, the slope

compensation is required in the traditional UC384X

design by injecting the ramp signal from the RT/CT pin

through a coupling capacitor. LD5762E/A has internal

slope compensation circuit to simplify the external circuit

design.

Oscillator and Switching Frequency

The LD5762E/A has the switching frequency between

65 kHz ±4kHz internally to optimize its performance in

EMI,

thermal

treatment,

component

sizes

and

transformer design.

Dual-Oscillator Green-Mode Operation

Many different topologies have been implemented in

different chips for the green-mode or power saving

requirements

such

“burst-mode

control

”,

“skipping-cycle mode”, “variable off-time control “…etc.

The basic operation theory of all these approaches

intended to reduce the switching cycles under light-load

or no-load condition either by skipping some switching

pulses or reducing the switching frequency.

By using LD proprietary dual-oscillator technique, the

green-mode frequency can be well controlled and

further to avoid the generation of audible noise.

Frequency Swapping

The LD5762E/A is built in with frequency swapping

function, which makes it easy for the power supply

designers to optimize EMI performance and system

cost.

On/Off Control

Pulling COMP pin below VZDC will immediately disable

the gate output of LD5762E/A. Remove the pull-low

signal to reset it.

Over Current Protection (OCP) - Auto

Recovery

Auto recovery of smart OCP protection is the feature of

LD5762E/A. Fig. 13 shows the waveform under fault

condition. The feedback system will force the voltage

loop toward the saturation and thus pull the voltage high

across COMP pin (VCOMP). When the VCOMP ramps

up and achieves the OCP threshold of 4.6V, staying for

longer than OCP delay time, the protection will be

activated. The delay time prevents the false-triggering

during power-on, turn-off transient.

VCC

UVLO(ON)

UVLO(OFF)

COMP

OCP

VOCP

OUT

OCP Delay Time

Switching

Non-Switching

OCP trip Level

2nd UVLO(OFF)

OCP Counter Reset

BNO

Detecting

Fig. 13

Over Voltage Protection on VCC (OVP)

–

Auto Recovery for LD5762E

The VGS ratings of the nowadays power MOSFETs are

mostly with 28.5V maximum. To protect the VGS from

the fault condition, LD5762E/A is implemented with OVP

function on VCC. As the VCC voltage is larger than the

OVP threshold voltage, the output gate drive circuit will

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