156869 Datasheet, PDF (7/9 Pages) Texas Instruments – Switched Capacitor Voltage Converter

Other Applications
PARALLELING DEVICES
Any number of LM2664s can be paralleled to reduce the
output resistance. Each device must have its own pumping
capacitor C₁, while only one output capacitor C_out is needed
as shown in Figure 3. The composite output resistance is:
FIGURE 3. Lowering Output Resistance by Paralleling Devices
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CASCADING DEVICES
Cascading the LM2664s 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 ef-
fective 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}
Note that, the number of n is practically limited since the
increasing of n significantly reduces the efficiency, and in-
creases the output resistance and output voltage ripple.
FIGURE 4. Increasing Output Voltage by Cascading Devices
COMBINED DOUBLER AND INVERTER
In Figure 5, the LM2664 is used to provide a positive voltage
doubler and a negative voltage converter. Note that the total
current drawn from the two outputs should not exceed 50
mA.
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