Rainbow Electronics MAX681 - Manual (Page 7)

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
V
CC , 10mA can be drawn from both regulated outputs
simultaneously. Assuming 150
Ω
source resistance for
both converters, with (I L+ + I L- ) = 20mA, the positive
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.
MAX680/MAX681
+5V to ±10V Voltage Converters
_______________________________________________________________________________________ 7
MAX680
100 µ F
10 µ F
0.1 µ F
100 µ F
100 µ F
+12V TO +6V
-12V TO -6V
0.1 µ F
10 µ F
100 µ F
C1+
GND
V CC
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
V IN
VOUT1
VOUT2
SENSE
SDN GND V SET
MAX664
Figure 5. Regulated +5V and -5V from a Single Battery