LD5525GL datasheet(13/16 Pages) LEADTREND

13 / 16 page

LD5525

06/30/2015

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5525-DS-00 June 2015

95uA

Vcc

OUT

Switching

Non-Switching

IFB

Line Voltage

80uA

Non-

Switching

Normal Range

UVLO(on)

UVLO(off)

Fig. 15

Over Voltage Protection on FB pin (FB

OVP)

– Auto Recovery

An output overvoltage protection is implemented in the

LD5525. The auxiliary winding voltage can be reflected

from secondary winding, in which the FB pin voltage is

proportional to output voltage during the gate off time.

OVP is worked by sensing the auxiliary voltage via the

divided resistors R2, refereeing to Fig. 14. The equation of

FB OVP is shown as follows.

��2 =

��1 ∙ ��_��

�� − ��_��

�� =

��

�� + ��

VFB_OVP is the FB pin OVP trip voltage level. Va is the

auxiliary winding voltage which reflects from the forward

voltage VF of Schottky diode and output voltage VO. NS is

turns ration of secondary-side winding.

If VFB overs the FB OVP trip level, the internal counter

starts counting 8 cycles, and then LD5525 goes to

auto-recovery protection mode till the FB OVP status is

defused

Under

Voltage

Protection

(FB UVP)

– Auto Recovery

In order to prevent output short situation, LD5525 is

implemented by FB_UVP. When the output load is

shorted to ground, the voltage suddenly decreases to zero,

which always reflects to auxiliary winding during the gate

off region. Therefore, as VFB is lower than 1V during gate

off region, and then the FB_UVP is triggered.

Over Temperature Protection on CS pin

(CS OTP)- Auto Recovery

LD5525 is implemented over temperature protection on

CS pin which senses voltage to determine NTC status

during gate off region. As VCS is greater than 0.5V and

continues for 8 cycles, CS_OTP is triggered, than LD5525

is in auto recovery mode till the temperature drops to

setting work condition.

Oscillator and Switching Frequency

The LD5525 is implemented with Frequency Swapping

function which helps the power supply designers to both

optimize EMI performance and lower system cost.

Green Mode Operation

By using the green-mode control, the switching frequency

can be reduced under the light load condition. This feature

helps to improve the efficiency in light load conditions.

The green-mode control is Leadtrend Technology

’s own

property.

Fault Protection

There are several critical protections integrated in the

LD5525 to prevent from damage to the power supply.

Those damages usually come from open or short

conditions on the pins of LD5525.

In case under such conditions listed below, the gate

output will turn off immediately to protect the power circuit.

CS pin floating

COMP pin floating

LD5525GL Datasheet(PDF) 13 Page - Leadtrend Technology

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