2.2µF, C

Power-Up Response

Power-Down Response

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Application Information

General Information

LP3982 is package, pin and performance compatible with

Maxim’s MAX8860 excluding reverse battery protection and

Figure 1 shows the functional block diagram for the LP3982.

A 1.25V bandgap reference, an error amplifier and a PMOS

pass transistor perform voltage regulation while being sup-

ported by shutdown, fault, and the usual Temperature and

current protection circuitry

The regulator’s topology is the classic type with negative

feedback from the output to one of the inputs of the error

amplifier. Feedback resistors R

external to the IC, depending on whether it is the fixed

voltage version or the adjustable version. The negative feed-

back and high open loop gain of the error amplifier cause the

two inputs of the error amplifier to be virtually equal in

voltage. If the output voltage changes due to load changes,

the error amplifier provides the appropriate drive to the pass

transistor to maintain the error amplifier’s inputs as virtually

equal. In short, the error amplifier keeps the output voltage

constant in order to keep its inputs equal.

Output Voltage Setting (ADJ version only)

The output voltage is set according to the amount of nega-

tive feedback (Note that the pass transistor inverts the feed-

back signal.) Figure 2 simplifies the topology of the LP3982.

This type of regulator can be represented as an op amp

configured as non-inverting amplifier and a fixed DC Voltage

(V

op amp is its extra-large output transistor that only sources

current. In terms of its non-inverting configuration, the output

voltage equals V

Utilize the following equation for adjusting the output to a

particular voltage:

Choose R

jection, noise and power consumption.

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FIGURE 1. Functional Block Diagram for the LP3982

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