THERMAL SHUTDOWN

1.25V

REFERENCE

GND

+

-

MOSFET

DRIVER

FOLDBACK CURRENT

LIMIT

VIN

P

VOUT

Fixed VOUT

R1

R2

ADJ

P

Adjustable

Version

DPAK Only

VOUT SENSE

ERROR

AMP

LP8340

SNVS221D – FEBRUARY 2003 – REVISED APRIL 2013

www.ti.com

APPLICATIONS SECTION

GENERAL INFORMATION

The LP8340 is a low-dropout, low quiescent current linear regulator. As shown in Figure 22 it consists of a 1.25V

reference, error amplifier, MOSFET driver, PMOS pass transistor and for the fixed output versions, an internal

feedback network (R1/R2). In addition, the device is protected from overload by a thermal shutdown circuit and a

foldback current limit circuit

The 1.25V reference is connected to the inverting input of the error amplifier. Regulation of the output voltage is

achieved by means of negative feedback to the non-inverting input of the error amplifier. Feedback resistors R1

and R2 are either internal or external to the device, depending on whether it is a 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 amp to be virtually equal in voltage. If the output voltage changes due to load changes, the error

amplifier and MOSFET driver provide the appropriate drive to the pass transistor to maintain the error amplifier’s

inputs as virtually equal.

Figure 22. LP8340 Functional Block Diagram

EXTERNAL CAPACITOR

An Input capacitor of 1

μF or greater is required between the LP8340 VIN pin and ground. While 1μF will provide

adequate bypassing of the VIN supply larger values of input capacitor (i.e. 10μF) can provide improved bypassing

of power supply noise.

Stable operation can be achieved with an output capacitor of 1

μF or greater, either ceramic X7R dielectric or

aluminum/tantalum electrolytic. While the minimum capacitor value is 1

μF, the typical output capacitor values

selected range from 1

μF to 10μF. The larger values provide improved load-transient response, power supply

rejection and stability.

10

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