+

Current

Limit

Thermal

Shutdown

IN

OUT

GND

VREF

800 mV

EN

OFF

ON

1 M



LP3990

LP3990

www.ti.com

SNVS251J – MAY 2004 – REVISED SEPTEMBER 2014

7 Detailed Description

7.1 Overview

Designed meet the requirements of portable, battery-powered digital systems providing an accurate output

voltage with fast start-up. When disabled via a low logic signal at the enable pin (EN), the power consumption is

reduced to virtually zero

The LP3990 is designed to perform with a single 1-

μF input capacitor and a single 1-μF ceramic output

capacitor.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Enable (EN)

The LP3990 Enable (EN) pin is internally held low by a 1-M

Ω resistor to GND. The EN pin voltage must be

higher than the VIH threshold to ensure that the device is fully enabled under all operating conditions. The EN pin

voltage must be lower than the VIL threshold to ensure that the device is fully disabled. If the EN pin is left open

the LP3990 output will be disabled.

7.3.2 Thermal Overload Protection (TSD)

Thermal Shutdown disables the output when the junction temperature rises to approximately 155°C which allows

the device to cool. When the junction temperature cools to approximately 140°C, the output circuitry enables.

Based on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may

cycle on and off. This thermal cycling limits the dissipation of the regulator and protects it from damage as a

result of overheating.

The Thermal Shutdown circuitry of the LP3990 has been designed to protect against temporary thermal overload

conditions. The Thermal Shutdown circuitry was not intended to replace proper heat-sinking. Continuously

running the LP3990 device into thermal shutdown may degrade device reliability.

Copyright © 2004–2014, Texas Instruments Incorporated

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