 2002 Microchip Technology Inc.

DS21358B-page 7

TC1121

3.6

Combined Positive Supply

Multiplication and Negative

Voltage Conversion

Figure 3-4 shows this dual function circuit, in which

capacitors C1 and C2 perform pump and reservoir

functions to generate negative voltage. Capacitors C3

and C4 are the respective capacitors for multiplied

positive voltage. This particular configuration leads to

higher source impedances of the generated supplies

due

to

the

finite

impedance

of

the

common

charge-pump driver.

FIGURE 3-4:

COMBINED POSITIVE MULTIPLER AND NEGATIVE CONVERTER

1

1

2

1, D2 = 1N4148

2

4

3

+

V

C1121

ND

SC

AP

AP

C

HDN

UT

N

HDN*

–