LM2662 datasheet(9/12 Pages) NSC

9 / 12 page

Other Applications

PARALLELING DEVICES

Any number of LM2662s (or LM2663s) can be paralleled to reduce the output resistance. Each device must have its own pumping

capacitor C

1, while only one output capacitor Cout is needed as shown in Figure 4. The composite output resistance is:

CASCADING DEVICES

Cascading the LM2662s (or LM2663s) 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

out is (−nVin). The effective output resistance

is equal to the weighted sum of each individual device:

A three-stage cascade circuit shown in

Figure 6 generates −3V

in, from Vin.

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

Figure 7, two devices are cascaded to generate 3V

in.

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.

DS100003-24

FIGURE 4. Lowering Output Resistance by Paralleling Devices

DS100003-25

FIGURE 5. Increasing Output Voltage by Cascading Devices

LM2662 Datasheet(PDF) 9 Page - National Semiconductor (TI)