LD5537GL datasheet(13/17 Pages) LEADTREND

13 / 17 page

LD5537

09/07/2015

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5537-DS-01 September 2015

OVP (Over Voltage Protection) on VCC -

Auto Recovery

The Vcc OVP function of LD5537 is in auto recovery

mode. As soon as the voltage of the Vcc pin rises above

OVP threshold, the output gate drive circuit will be

shutdown simultaneous to turn off the power MOSFET.

Fig. 20 shows its operation.

VCC

OVP

UVLO(off)

OVP Reset

OUT

Switching

Non- Switching

OVP

Level

UVLO (on)

UVLO (off)

Fig. 20

Brownout Protection

The LD5537 is programmable for the brownout protection

point though BNO pin. The voltage across the BNO pin is

proportional to the bulk capacitor voltage, referred as the

line voltage.

A brownout comparator is implemented to

detect the abnormal line condition. As soon as the

condition is detected, it will shut down the controller to

prevent the damage.

Fig. 21 shows the operation.

When VBNO falls below 1.30V, the gate output will remain

off even as VCC achieved UVLO(ON). It therefore makes

VCC hiccup between UVLO(ON) and UVLO(OFF).

Unless the line voltage is large enough to pull VBNO over

1.40V, the gate output will not start switching even when

the

UVLO(ON)

tripped.

hysteresis

implemented to prevent the false trigger during turn-on

and turn-off.

Fig. 21

Adjustable Over Power Compensation (CS

Pin)

In general, the power converter can deliver more current

with high input voltage than low input voltage. To

compensate this, an offset voltage is added to the CS

signal by an internal current source (IOPP) and an external

resistor (ROPP) in series between the sense resistor (Rs)

and the CS pin, as shown in Fig. 22. Different values of

resistors in series with the CS pin may adjust the amount

of compensation. The value of IOPP depends on the duty

cycle of OUT pin. The equation of IOPP is decreased as:























)

Duty

(

575

)

Duty

(

)

Duty

(

1915

)

Duty

(

IOPP

In light load, this offset is in same level of magnitude as

the current sense signal, it shall be canceled. Therefore

1.40V

VCC

OUT

Switching

Non-Switching

VBNO

Line Voltage

1.30V

Non-

Switching

Normal Range

UVLO(ON)

UVLO(OFF)

LD5537GL датащи(PDF) 13 Page - Leadtrend Technology

LD5537GL датащи(HTML) 13 Page - Leadtrend Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

датащи скачать

ссылки URL