TC1221/TC1222

DS21367B-page 8

 2002 Microchip Technology Inc.

4.9

Voltage Doubler/Inverter

Another common application of the TC1221/TC1222 is

shown in Figure 4-6. This circuit performs two functions

in combination. C1 and C2 form the standard inverter

circuit described above. C3 and C4 plus the two diodes

form the voltage doubler circuit. C1 and C3 are the

pump capacitors and C2 and C4 are the reservoir

capacitors. Because both sub-circuits rely on the same

switches if either output is loaded, both will droop

toward GND. Make sure that the total current drawn

from both the outputs does not total more than 40mA.

4.10

Diode Protection for Heavy Loads

When heavy loads require the OUT pin to sink large

currents being delivered by a positive source, diode

protection may be needed. The OUT pin should not be

allowed

to

be

pulled

above

ground.

This

is

accomplished

by

connecting

a

Schottky

diode

(1N5817) as shown in Figure 4-7.

4.11

Layout Considerations

As with any switching power supply circuit, good layout

practice is recommended. Mount components as close

together as possible to minimize stray inductance and

capacitance. Noise leakage into other circuitry can be

minimized with the use of a large ground plane.

FIGURE 4-6:

COMBINED DOUBLER AND INVERTER

FIGURE 4-7:

HIGH V– LOAD CURRENT

C1

D1

D2

D1, D2 = 1N4148

6

4

1

2

3

C2

C4

C3

TC1221

TC1222

Shutdown

Control

5

+

+

+

+

TC1221

TC1222

GND

OUT

4

1