CASCADING DEVICES

Cascading the LM2660s (or LM2661s) is an easy way to produce a greater negative voltage (as shown in

Figure 5). If n is the

integer representing the number of devices cascaded, the unloaded output voltage V

is equal to the weighted sum of each individual device:

A three-stage cascade circuit shown in

Figure 6 generates −3V

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

Figure 7, two devices are cascaded to generate 3V

An example of using the circuit in

Figure 6 or Figure 7 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.

DS012911-23

FIGURE 5. Increasing Output Voltage by Cascading Devices

DS012911-24

FIGURE 6. Generating −3V

DS012911-25

FIGURE 7. Generating +3V

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