LD9532 datasheet(13/17 Pages) LEADTREND

13 / 17 page

LD9532

12/11/2018

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD9532-DS-00 December 2018

Vcc

OUT

Switching

Non-Switching

IFB

Line Voltage

Non-

Switching

Normal Range

UVLO(on)

UVLO(off)

95µA

85µA

VDC_BNI =

∙ IBNI ∙ R1

VDC_BNO =

∙ IBNO ∙ R1

,where

VDC_BNI is predicted BNI DC value of input voltage.

VDC_BNO is predicted BNO DC value of input voltage.

IBNI is BNI trip current.

IBNO is BNO trip current.

Np is turns ration of primary-side winding.

Na is turns ration of auxiliary winding.

Fig. 18

Fig. 19

Over Voltage Protection on FB pin (FB

OVP)

– Auto Recovery

An output overvoltage protection is implemented in the

LD9532. 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. 18. The equation

of FB OVP is shown as follows.

R2 =

R1 ∙ VFB_OVP

Va − VFB_OVP

Va =

VO + VF

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 LD9532 goes to

auto-recovery protection mode till the FB OVP status is

defused.

Output Short Circuit Protection (OSCP)

–

Auto Recovery

The OSCP function can prevent the damage from

output short circuit. Once the output is shorted, Vo and

VCC drop immediately,

which always reflects the

auxiliary winding during the gate off region. Therefore,

as VFB is lower than 0.8V during gate off region, then the

FB_UVP is triggered, and skips one cycle. According to

the close loop control, COMP voltage will pull high in the

meanwhile. If the VCOMP pulls higher than 2.8V over

15 ms and Vcc drops below 9.6V. At this time, the OSCP

protection will be triggered and turn off the gate driving.

Oscillator and Switching Frequency

The LD9532 is implemented with frequency swapping

function which helps the power supply designers to both

optimize EMI performance and lower system cost.

LD9532

VCC

GND

VFB

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