The MAX680/MAX681 are not voltage regulators: the

output source resistance of either charge pump is

approximately 150

approach +10V and V- will be at -10V. However both,

V+ and V- will droop toward GND as the current drawn

from either V+ or V- increases, since the negative con-

verter draws its power from the positive converter’s out-

put. To predict output voltages, treat the chips as two

separate converters and analyze them separately. First,

of the negative converter (RS-):

the positive converter’s source resistance (RS+),

except that the current drawn from the positive supply

is the sum of the current drawn by the load on the posi-

The positive output voltage will be:

The negative output voltage will be:

The positive and negative charge pumps are tested

and specified separately to provide the separate values

of output source resistance for use in the above formu-

las. When the positive charge pump is tested, the neg-

ative charge pump is unloaded. When the negative

charge pump is tested, the positive supply V+ is from

an external source, isolating the negative charge

pump.

Calculate the ripple voltage on either output by noting

that the current drawn from the output is supplied by

the reservoir capacitor alone during one half-cycle of

the clock. This results in a ripple of:

Remember that in most applications, the positive

taken by the negative charge pump.

+5V to ±10V Voltage Converters

6

_______________________________________________________________________________________

MAX680

22

µF

22

µF

C1-

8

7

6

5

C2+

V-

V+

1

2

3

4

C1+

GND

C2-

MAX680

22

µF

22

µF

22

µF

V+ OUT

V- OUT

GND

22

µF

C1-

8

7

6

5

C2+

V-

V+

1

2

3

4

C1+

GND

C2-

Figure 4. Paralleling MAX680s For Lower Source Resistance