LD5760GS datasheet(14/20 Pages) LEADTREND

14 / 20 page

LD5760

11/05/2015

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5760-DS-02 November 2015

some

switching

pulses

reduce

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 LD5760 is built in with frequency swapping function,

which makes it easy for the power supply designers to

optimize EMI performance and system cost.

The

frequency swapping is internally set for

8%.

On/Off Control

Pulling COMP pin below VFB_B will immediately disable

the gate output of LD5760. Remove the pull-low signal

to reset it.

Over Load Protection (OLP)- Auto

Recovery

To protect the circuit from being damaged during over

load condition and short or open loop condition, the

LD5760 is implemented with smart OLP function.

LD5760 features auto recovery function of it, see Fig. 17

for the waveform. In the example of the fault condition,

the feedback system will force the voltage loop enter

toward the saturation and then pull the voltage high on

COMP pin (VCOMP).

When the VCOMP ramps up to the

OLP tripped level (4.6V) and stays for more than the

OLP delay time, the protection will be activate and then

turn off the gate output to stop the switching of power

circuit. The OLP delay time is set by internal high

frequency counter. It is to prevent the false triggering

from the power-on and turn-off transient.

A divide-2 counter is implemented to reduce the

average power under OLP behavior.

As soon as OLP

is activated, the output will be latched off and the

divide-2 counter will start to count the number of

UVLO(OFF).

The latch will not be released until the

3rd UVLO(OFF) point is counted, after that the output

will resume to switch again. With the protection

mechanism, the average input power will be minimized,

so that the component temperature and stress can be

controlled within the safe operating area.

VCC

VCC-ON

VCC-OFF

COMP

OLP

VOLP

OUT

OLP Delay Time

Switching

Non-Switching

OLP trip Level

2nd UVLO(off)

OLP Counter Reset

BNO

Detecting

Fig. 17

OVP (Over Voltage Protection) on VCC

–

Auto Recovery

The maximum VCC ratings of the LD5760 are mostly for

30V. To prevent the controller enter fault condition,

LD5760 series are implemented with OVP function on

VCC.

Whenever the VCC voltage is higher than the

OVP threshold, the output gate drive circuit will be

shutdown simultaneously and the switching of the power

MOSFET is disabled until the next two UVLO(ON).

The

VCC

OVP

functions

LD5760

are

auto-recoverable.

If the OVP condition, usually caused

by open-loop of feedback, is not released, the VCC will

tripped the OVP level again and re-shutdown the output.

The VCC works in hiccup mode. Figure 18 shows its

operation.

Otherwise, when the OVP condition is removed, the

VCC level will be resumed and the output will

automatically return to the normal operation.

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