FA7622CP(E)

5

• Inverting chopper circuit

According to the circuit shown in Fig. 5, the power output

(5)

..............................

as follows:

(6)

.................................................

By using this circuit, invert the output polarity of OUT2 with an

external transistor to drive a P-channel MOSFET (or PNP

transistor).

3. PWM comparator section

As Fig. 6 shows, a PWM comparator has three input

terminals. PWM comparator 1 determines the duty cycle of

the output from the OUT1 pin. This comparator compares the

the DT1 voltage (Pin 16), whichever is greater. When the

output is low.

PWM comparator 2 determines the duty cycle of the output

from the OUT2 pin. To determine the PWM output, this

FB2 voltage (Pin 6) or the DT2 voltage (Pin 7) whichever is

higher.

During ordinary operation, the OUT1 and OUT2 pin voltages

have the same polarity as the output from each comparator.

When the power supply is turned on, the pulse width

gradually increases. The time constant for soft-start is

determined by the external resistor and capacitor across pins

16 and 7. In Figures 7 and 8, the time ts required for the pulse

width (duty-cycle) to reach about 30% after start-up can be

determined as follows:

(Units:

µF for Cs and kΩ for Rs, Rs1, and Rs2)

Fig. 5

Fig. 8

Fig. 6

C3

Q3

FB2

R10

R9

REF

R11

R12

R13

IN2

IN2

ER.AMP2

+

-

10

20

6

5

4

OUT2

PWM output

FB1(FB2)

DT1(DT2)

Time

CT

PWM output

PWM1

(PWM2)

DT1(DT2)

FB1(FB2)

CT

Fig. 7

DT1(DT2)

20

1

FB1(FB2)

CT

REF

PWM output

PWM1

(PWM2)

20

1

DT1(DT2)

FB1(FB2)

CT

REF

PWM output

PWM1

(PWM2)

Fig.8:

• ln

(7)

.................................

Fig.7:

(8)

……

Please connect enough large capacitance between REF and

GND pins in order to prevent irregular output pulse caused by

minus voltage at DT1 or DT2 pin when IC is shut down.