PWM section

PM8800A

24/35

When a shunt regulator is used for output voltage regulation, the output voltage is set by the

ratio of resistors R1 and R2, see Figure 14 for details. The output voltage is given by the

following equation:

Loop compensation in typical isolated application is done by connecting an appropriate

compensation network around the external error amplifier.

A pull-up current source of few nA is internally connected to FB pin providing a safe switch-

off of the DC DC converter in case of feedback disconnection.

6.2

Oscillator and sync capability

The internal oscillator frequency can be programmed by connecting an external resistor

Figure 15.

The PWM switching frequency is equal to the programmed oscillator frequency.

V

out

V

REF

1

R

2

R

1

-------

+

⎝⎠

⎛⎞

⋅

=

f

()

100

1

125

3k

Ω R

+

()

--------------------------------------

+

⎝⎠

⎛⎞

⋅

=

0

100

200

300

400

500

600

700

800

900

1000

0

100

200

300

400

RT [kOhm ]