A three-stage cascade circuit shown in

Figure 7 generates −3V

Cascading is also possible when devices are operating in doubling mode. In

Figure 8, two devices are cascaded to generate 3V

An example of using the circuit in

Figure 7 or Figure 8 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.

REGULATING V

out

It is possible to regulate the output of the MAX660 by use of a low dropout regulator (such as LP2951). The whole converter is

depicted in

Figure 9. This converter can give a regulated output from −1.5V to −5.5V by choosing the proper resistor ratio:

where

DS100898-8

FIGURE 6. Increasing Output Voltage by Cascading Devices

DS100898-9

FIGURE 7. Generating −3V

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FIGURE 8. Generating +3V

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