TPS9111

CELLULAR SUBSCRIBER TERMINAL

POWER SUPPLY

SLVS134A – NOVEMBER 1996 – REVISED APRIL 1998

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

charge-pump design (continued)

The output voltage for the doubler is then:

VO + 2

VCC * 2

Vdiode * IO

Rtotal

and the output voltage for the inverter is:

VO +* (VCC * 2

Vdiode) ) IO

Rtotal

To determine the size of C1 use:

C

+

I

f

DV

where f = 100,000 and

∆V = ripple voltage.

For an output current of 10 mA calculate:

C1

+

0.01 A

100 kHz

0.1 Vripple

+ 1 mF

Because of losses caused by diode switching and ESR, the calculated capacitance should be multiplied by 1.5

to 2. A 2-

µF capacitance should drive a 10-mA voltage doubler or inverter.