156869 Datasheet, PDF (8/9 Pages) Texas Instruments – Switched Capacitor Voltage Converter

Other Applications (Continued)
FIGURE 5. Combined Voltage Doubler and Inverter
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REGULATING V_OUT
It is possible to regulate the negative output of the LM2664
by use of a low dropout regulator (such as LP2980). The
whole converter is depicted in Figure 6. This converter can
give a regulated output from −1.8V to −5.5V by choosing the
proper resistor ratio:
V_out = V_ref (1 + R₁/R₂)
where, V_ref = 1.23V
Note that, the following conditions must be satisfied simulta-
neously for worst case design:
> V_{in_min} V_{out_min} +V_{drop_max} (LP2980)
+ I_{out_max} x R_{out_max} (LM2664)
< V_{in_max} V_{out_max} +V_{drop_min} (LP2980)
+ I_{out_min} x R_{out_min} (LM2664)
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FIGURE 6. Combining LM2664 with LP2980 to Make a Negative Adjustable Regulator
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