O

1

2

V

R

R

1

1.25V

é

ù

=

-

ê

ú

ë

û

+ 1

OFF

THERMAL

PROTECTION

1.25V

BANDGAP

FAST

START-UP

CIRCUIT

CURRENT

LIMIT

FAULT

COMPARATORS

R1

R2

SET

CC

SHDN

FAULT

GND

ERROR

AMP

+

-

LP3982

www.ti.com

SNVS185D – FEBRUARY 2002 – REVISED APRIL 2013

APPLICATION INFORMATION

General Information

The LP3982 is package, pin and performance compatible with Maxim's MAX8860 excluding reverse battery

protection and Dual Mode function (fixed and adjustable combined).

Figure 16 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 supported 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

the fixed voltage version or the adjustable version. The negative feedback 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.

Figure 16. Functional Block Diagram for the LP3982

Output Voltage Setting (Adj Version Only)

The output voltage is set according to the amount of negative feedback (Note that the pass transistor inverts the

feedback signal.) Figure 17 simplifies the topology of the LP3982. This type of regulator can be represented as

characteristic of this op amp is its extra-large output transistor that only sources current. In terms of its non-

(1)

Utilize the following equation for adjusting the output to a particular voltage:

(2)

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