Cascading Devices

Devices can be cascaded to produce an even larger

voltage (Figure 3). The unloaded output voltage is nom-

doublers used. This voltage is reduced by the output

resistance of the first device multiplied by the quiescent

current of the second. The output resistance increases

when devices are cascaded. Using a two-stage dou-

bler as an example, output resistance can be approxi-

output resistance of the second stage. A typical value

for a two-stage voltage doubler is 60

Ω (with C1 at 10µF

for MAX1682 and 3.3µF for MAX1683). For n stages

Paralleling Devices

Paralleling multiple MAX1682 or MAX1683s reduces

the output resistance. Each device requires its own

pump capacitor (C1), but the reservoir capacitor (C2)

serves all devices (Figure 4). Increase C2’s value by a

factor of n, where n is the number of parallel devices.

Figure 4 shows the equation for calculating output

resistance.

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.

Switched-Capacitor Voltage Doublers

_______________________________________________________________________________________

7

MAX1682

MAX1683

C1

C2

C2

C1+

IN

OUT

GND

C1-

MAX1682

MAX1683

C1

C1+

INPUT

SUPPLY

VOLTAGE

OUTPUT

VOLTAGE

IN

OUT

GND

C1-

Figure 3. Cascading Devices

MAX1682

MAX1683

NUMBER OF DEVICES

C2

C1+

IN

OUT

GND

C1-

MAX1682

MAX1683

C1

C1

C1+

INPUT

SUPPLY

VOLTAGE

OUTPUT

VOLTAGE

IN

OUT

GND

C1-

Figure 4. Paralleling Devices