5

TCM828/829-4 5/22/00

TCM828

TCM829

Switched Capacitor

Voltage Converters

© 2001 Microchip Technology Inc.

DS21488A

Diode Protection for Heavy Loads

When heavy loads require the OUT pin to sink large

currents being delivered by a positive source, diode protec-

tion may be needed. The OUT pin should not be allowed to

be pulled above ground. This is accomplished by connect-

ing a Schottky diode (1N5817) as shown in Figure 7.

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. Also use a large ground plane to minimize

noise leakage into other circuitry.

Voltage Doubler/Inverter

Another common application of the TCM828/829 is

shown in Figure 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.

Figure 6. Combined Doubler and Inverter

C1

D1

D2

D1, D2 = 1N4148

5

4

1

2

3

C2

C4

C3

V

IN

+

V

–

V

(V

TCM828

TCM829

TCM828

TCM829

GND

OUT

4

1

Figure 5. Paralleling TCM828s or TCM829s to Reduce Output Resistance

C1

C1

5

5

4

3

4

1

2

2

1

3

C2

V

OUT

V

R

OUT =

R

OUT

OF SINGLE DEVICE

V

IN

+

NUMBER OF DEVICES

–

TCM828

TCM829

"1"

TCM828

TCM829

"n"

. . .

. . .

. . .