Datasheet > EM8632

EM8632

更新时间： 2022-06-24 15:41:51

品牌	Logo	应用领域
杰力科技 - EXCELLIANCE		/
页数	文件大小	规格书
11页	285K
描述
Green mode PWM Flyback Controller

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EM8632 数据手册

EM8632

Functional Description

UVLO

An UVLO comparator is implemented in EM8632 to

monitor the VDD pin voltage. As shown in Fig. 11, a

hysteresis is built in to prevent the shutdown from

the voltage drop during startup. The UVLO (on) and

UVLO (off) are setting at 15V and 9.8V,

respectively.

Fig. 12

Switching Frequency

To guarantee accurate frequency, EM8632 is

trimmed to 5% tolerance. The internal oscillator

also generates slope compensation, 75% maximum

duty limit. Connect a resistor form RT pin to GND

according to equation below to program the

switching frequency:

Fig. 11

Startup Operation

Fig. 12 shows a typical startup circuit and

transformer auxiliary winding for the EM8632

application, it consumes only startup current

(typical 6uA) and the current supplied through the

startup resistor charges the VDD capacitor (C_VDD).

When VDD reaches UVLO (on) voltage, EM8632

begins switching and the current consumed

increases to 2mA. Then, the power required is

supplied from the transformer auxiliary winding.

The hysteresis of UVLO (off) provides more holdup

time, which allows using a small capacitor for VDD.

The ultra low startup current (typical 6uA) allow

system using higher resistance value of R_Start. It

provides a fast startup and low power dissipation

solution.

f_sw(KHz)= 6500/RT(KΩ)

Leading Edge Blanking (LEB)

Each time the power MOSFET turn on, the MOSFET

C_OSS, secondary rectifier reverse recovery current

and gate driver sourcing current comprise the

current spike. To avoid premature termination of

the switching pulse, a leading edge blanking time is

built in. During the blanking time (300nS), the

PWM comparator is off and cannot switch off the

gate driver. It is recommended to adopt a smaller

R-C filter (as show ad Fig.13) for high power

application to avoid the total spike width over

300nS leading edge blanking time.

2013/01/30

A.2

1...4 5 678 9 10 11

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