Application Information
(Continued)
(Continued)
Capacitor Type
Ceramic chip capacitors
Ceramic chip capacitors
Ceramic chip capacitors
Low ESR Capacitor Manufacturers
Manufacturer
Murata
Taiyo Yuden
Tokin
Phone
(800)-831-9172
(800)-348-2496
(408)-432-8020
Other Applications
Paralleling Devices
Any number of LM828s can be paralleled to reduce the out-
put resistance. Each device must have its own pumping ca-
pacitor C
1
, while only one output capacitor C
out
is needed as
shown in Figure 3. The composite output resistance is:
DS100137-9
FIGURE 3. Lowering Output Resistance by Paralleling Devices
Cascading Devices
Cascading the LM828s is an easy way to produce a greater
negative voltage (e.g. A two-stage cascade circuit is shown
in Figure 4).
If n is the integer representing the number of devices cas-
caded, the unloaded output voltage V
out
is (-nV
in
). The effec-
tive output resistance is equal to the weighted sum of each
individual device:
R
out
= nR
out_1
+ n/2 R
out_2
+ ... + R
out_n
This can be seen by first assuming that each device is 100
percent efficient. Since the output voltage is different on
each device the output current is as well. Each cascaded de-
vice sees less current at the output than the previous so the
R
OUT
voltage drop is lower in each device added. 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.
DS100137-10
FIGURE 4. Increasing Output Voltage by Cascading Devices
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