+

Current

Limit

Thermal

Shutdown

IN

OUT

GND

800 mV

EN

OFF

ON

1 M

LP3990

LP3990-Q1

www.ti.com

SNVSA66A – OCTOBER 2014 – REVISED DECEMBER 2015

7 Detailed Description

7.1 Overview

The LP3990-Q1 is designed to 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 device 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-Q1 Enable (EN) pin is internally held low by a 1-M

Ω resistor to GND. The EN pin voltage must be

the LP3990-Q1 output is disabled.

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-Q1 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-Q1 device into thermal shutdown may degrade device reliability.

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