Paralleling Devices

Paralleling multiple MAX680/MAX681s reduces the out-

put resistance of both the positive and negative con-

verters. The effective output resistance is the output

resistance of a single device divided by the number of

devices. As Figure 4 shows, each MAX680 requires

separate pump capacitors C1 and C2, but all can

share a single set of reservoir capacitors.

±5V Regulated Supplies from

a Single 3V Battery

Figure 5 shows a complete ±5V power supply using one

3V battery. The MAX680/MAX681 provide +6V at V+,

which is regulated to +5V by the MAX666, and -6V,

which is regulated to -5V by the MAX664. The MAX666

and MAX664 are pretrimmed at wafer sort and require

no external setting resistors, minimizing part count. The

combined quiescent current of the MAX680/MAX681,

MAX663, and MAX664 is less than 500µA, while the out-

put current capability is 5mA. The MAX680/MAX681

input can vary from 3V to 6V without affecting regulation

appreciably. With higher input voltage, more current can

be drawn from the MAX680/MAX681 outputs. With 5V at

simultaneously. Assuming 150

Ω source resistance for

charge pump will droop 3V, providing +7V for the nega-

tive charge pump. The negative charge pump will droop

another 1.5V due to its 10mA load, leaving -5.5V at V-

sufficient to maintain regulation for the MAX664 at this

current.

+5V to ±10V Voltage Converters

_______________________________________________________________________________________

7

MAX680

100

µF

10

µF

0.1

µF

100

µF

100

µF

+12V TO +6V

-12V TO -6V

0.1

µF

10

µF

100

µF

C1+

GND

C1-

C2-

V+

LBI

LOW-BATTERY

WARNING AT 3.5V

SENSE

VOUT

VIN

6V TO 3V

2M

Ω

1.2M

Ω

+5V

-5V

GND

LBO

SDN

GND

VSET

V-

C2+

MAX666

VOUT1

VOUT2

SENSE

SDN

GND

MAX664

Figure 5. Regulated +5V and -5V from a Single Battery