PJ3844B Просмотр технического описания (PDF) - Promax Johnton

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PJ3844B

High Performance Current Mode Controller

Promax Johnton 

PJ3844B / PJ3845B

High Performance Current Mode Controller

FIGURE 17-REPRESENTATIVE BLOCK DIAGRAM

Pin numbers adjacent to terminals are for the 8 pin dual-in-line package.

Pin numbers in parenthesis are for the SOP-14 package.

FIGURE 18-TIMING DIAGRAM

UNDERVOLTAGE LOCKOUT

Two undervoltage lockout comparators have been

incorporated to guarantee that the IC is fully functional before

the output stage is enabled. The positive power supply

terminal (VCC) and the reference output (Vref) are each

monitored by separate comparators.Each has built-in

hysteresis to prevent erratic output behavior as their respective

thresholds are crossed.The VCC comparator upper and lower

thresholds are 1 8.4 V/7.6 V for the UC3845A

The Vref comparator upper and lower thresholds are

3.6V/3.4V.The large hysteresis and low start-up current of the

UC3844B makes it ideally suited in off-line converter

applications where efficient bootstrap start-up technique

(Figure 33). 36 V zener is connected as a shunt regulator from

VCC to ground.Its purpose is to protect the IC from excessive

voltage that can occur during system start-up. The minimum

operating voltage for the UC3844B is 11V.

7-14

2004/11. Rev B

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