LD7750A View Datasheet(PDF) - Unspecified

Part Name

Description

Manufacturer

LD7750A

High Voltage Green-Mode PWM Controller with Over Temperature Protection

Unspecified 

LD7750A

A divided-by-2 counter is implemented to reduce the

average power consumption under OLP behavior. Once

OLP is activated, the output is latched off and the

divided-by-2 counter starts to count the number of

UVLO(off). The latch will be released if the 2nd UVLO(off)

point is counted, and then the output recovers switching

again.

By using such protection mechanism, the average input

power can be reduced to a very low level so that the

component temperature and stress can be controlled

within a safe operating area.

The Vcc OVP function in LD7750A is latched-off type of

protection. If the OVP condition (usually caused by the

feedback loop opened) is tripped, the Vcc will not recover

until ac power turn off. Figure 18 shows its operation. The

Vcc will drop if AC power turns off. The de-latch level of

OVP is defined by internal PDR. Over voltage protection

will be released after Vcc drops below PDR level.

Fig. 18

Fig. 17

OVP (Over Voltage Protection) on Vcc-

Latched Mode Protection

The VGS ratings of the nowadays power MOSFETs are

mostly with 30V maximum. To protect the VGS from the

fault condition, LD7750A is implemented with OVP

function on Vcc. As soon as Vcc voltage is larger than

the OVP threshold voltage, the output gate drive circuit

will be shut down simultaneously and stop switching of the

power MOSFET.

OTP Pin --- Latched Mode Protection

To protect the power circuit from damage due to system

failure, the over temperature protection (OTP) is required.

The OTP circuit is implemented to sense a hot-spot of

power circuit like power MOSFET or output rectifier. It

can be easily achieved by connecting a NTC with OTP pin

of LD7750A. As the device temperature or ambient

temperature rises, the resistance of NTC decreases. So,

the voltage on the OTP pin could be written as below.

VOTP = 100μA ⋅ RNTC

When the VOTP is less than the defined threshold voltage

(typical 0.95V), LD7750A will shutdown the gate output

Leadtrend Technology Corporation

LD7750A-DS-00 June 2010

12

www.leadtrend.com.tw

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