5

TC828A

Switched Capacitor

Voltage Converters

TC828A-1 5/1/00

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 TC828A 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 40 mA.

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

TC828

TC828

GND

OUT

4

1

Figure 5. Paralleling TC828As 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

–

TC828

“1”

TC828

“N”

. . .

. . .