Switched-Capacitor Voltage Inverters

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7

Combined Doubler/Inverter

In the circuit of Figure 6, capacitors C1 and C2 form the

inverter, while C3 and C4 form the doubler. C1 and C3

are the pump capacitors; C2 and C4 are the reservoir

capacitors. Because both the inverter and doubler use

part of the charge-pump circuit, loading either output

causes both outputs to decline toward GND. Make sure

the sum of the currents drawn from the two outputs

does not exceed 40mA.

Heavy Output Current Loads

When under heavy loads, where higher supply is sourc-

ing current into OUT, the OUT supply must not be pulled

above ground. Applications that sink heavy current into

OUT require a Schottky diode (1N5817) between GND

and OUT, with the anode connected to OUT (Figure 7).

Layout and Grounding

Good layout is important, primarily for good noise per-

formance. To ensure good layout, mount all compo-

nents as close together as possible, keep traces short

to minimize parasitic inductance and capacitance, and

use a ground plane.

MAX828

MAX829

“n”

MAX828

MAX829

“1”

2

1

C2

2

C1

C2

C1

3

3

4

4

5

5

1

…

…

Figure 4. Cascading MAX828s or MAX829s to Increase

Output Voltage

MAX870

MAX871

“n”

MAX870

MAX871

“1”

2

1

C2

2

C1

C1

3

3

4

4

5

5

1

NUMBER OF DEVICES

…

…

Figure 5. Paralleling MAX828s or MAX829s to Reduce Output

Resistance

MAX828

MAX829

2

1

C2

C1

3

4

5

C4

D1

D1, D2 = 1N4148

C3

D2

Figure 6. Combined Doubler and Inverter

MAX870

MAX871

4

1

GND

OUT

Figure 7. High V- Load Current