Other Applications

Paralleling Devices

Any number of LM2767s can be paralleled to reduce the out-

put resistance. Since there is no closed loop feedback, as

found in regulated circuits, stable operation is assured. Each

device must have its own pumping capacitor C

one output capacitor C

The composite output resistance is:

Cascading Devices

Cascading the LM2767s is an easy way to produce a greater

voltage (A two-stage cascade circuit is shown in Figure 4).

The effective output resistance is equal to the weighted sum

of each individual device:

R

Note that increasing the number of cascading stages is prac-

itically limited since it significantly reduces the efficiency, in-

creases the output resistance and output voltage ripple.

Regulating V

OUT

It is possible to regulate the output of the LM2767 by use of

a low dropout regulator (such as LP2980-5.0). The whole

converter is depicted in Figure 5.

A different output voltage is possible by use of LP2980-3.3,

LP2980-3.0, or LP2980-adj.

Note that the following conditions must be satisfied simulta-

neously for worst case design:

2V

in_min

2V

DS101274-19

FIGURE 3. Lowering Output Resistance by Paralleling Devices

DS101274-20

FIGURE 4. Increasing Output Voltage by Cascading Devices

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