Switched-Capacitor Voltage Inverters

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7

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

Under heavy loads, where higher supply is sourcing cur-

rent 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.

MAX870

MAX871

“n”

MAX870

MAX871

“1”

2

1

C2

2

C1

C2

C1

3

3

4

4

5

5

1

…

…

Figure 4. Cascading MAX870s or MAX871s 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 MAX870s or MAX871s to Reduce Output

Resistance

MAX870

MAX871

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