Datasheet

LM2660
www.ti.com SNVS135D –SEPTEMBER 1999–REVISED MAY 2013
CASCADING DEVICES
Cascading the LM2660s is an easy way to produce a greater negative voltage (as shown in Figure 19). 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:
(5)
A three-stage cascade circuit shown in Figure 20 generates −3V
in
, from V
in
.
Cascading is also possible when devices are operating in doubling mode. In Figure 21, two devices are
cascaded to generate 3V
in
.
An example of using the circuit in Figure 20 or Figure 21 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 output resistance and output voltage ripple.
Figure 19. Increasing Output Voltage by Cascading Devices
Figure 20. Generating −3V
in
from +V
in
Figure 21. Generating +3V
in
from +V
in
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