Other Applications
PARALLELING DEVICES
Any number of LM2662s (or LM2663s) can be paralleled to reduce the output resistance. Each device must have its own pumping
capacitor C
1
, while only one output capacitor C
out
is needed as shown in
Figure 4.
The composite output resistance is:
DS100003-24
FIGURE 4. Lowering Output Resistance by Paralleling Devices
CASCADING DEVICES
Cascading the LM2662s (or LM2663s) is an easy way to produce a greater negative voltage (as shown in
Figure 5).
If n is the
integer representing the number of devices cascaded, the unloaded output voltage V
out
is (−nV
in
). The effective output resistance
is equal to the weighted sum of each individual device:
A three-stage cascade circuit shown in
Figure 6
generates −3V
in
, from V
in
.
Cascading is also possible when devices are operating in doubling mode. In
Figure 7,
two devices are cascaded to generate 3V
in
.
An example of using the circuit in
Figure 6
or
Figure 7
is generating +15V or −15V from a +5V input.
Note that, the number of n is practically limited since the increasing of n significantly reduces the efficiency and increases the out-
put resistance and output voltage ripple.
DS100003-25
FIGURE 5. Increasing Output Voltage by Cascading Devices
9
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