LP3983

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SNVS213A – MAY 2004 – REVISED MARCH 2013

APPLICATION HINTS

POWER DISSIPATION AND DEVICE OPERATION

The permissible power dissipation for any package is a measure of the capability of the device to pass heat from

the power source, the junctions of the IC, to the ultimate heat sink, the ambient environment. Thus the power

dissipation is dependent on the ambient temperature and the thermal resistance across the various interfaces

between the die and ambient air.

As stated in the Electrical Characteristics section, the allowable power dissipation for the device in a given

package can be calculated using the equation:

PD = (TJ - TA)/θJA

(1)

With a

θJA = 255°C/W, the device in the DSBGA package returns a value of 392mW with a maximum junction

temperature of 125°C and an ambient temperature of 25°C. The actual power dissipation across the device can

be represented by the following equation:

PD = (VIN - VOUT) * IOUT

(2)

This establishes the relationship between the power dissipation allowed due to thermal considerations, the

voltage drop across the device, and the continuous current capability of the device. These two equations should

be used to determine the optimum operating conditions for the device in the application.

EXTERNAL CAPACITORS

In common with most low-dropout regulators, the LP3983 requires external capacitors to ensure stable operation.

The LP3983 is specifically designed for portable applications requiring minimum board space and smallest

components. These capacitors must be correctly selected for good performance.

INPUT CAPACITOR

An input capacitor is required for stability. It is recommended that a 1.0uF capacitor be connected between the

LP3983 input pin and ground (this capacitance value may be increased without limit).

This capacitor must be located a distance of not more than 1cm from the input pin and returned to a clean

analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.

Important: Tantalum capacitors can suffer catastrophic failures due to surge current when connected to a low-

impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input,

it must be guaranteed by the manufacturer to have a surge current rating sufficient for the application.

There are no requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance and

temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will be

≊ 1µF

over the entire operating temperature range.

OUTPUT CAPACITOR

The LP3983 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor

(dielectric types Z5U, Y5V or X7R), recommended value 2.2µF and with ESR between 5m

Ω to 500mΩ, is

suitable in the LP3983 application circuit.

For this device the output capacitor should be connected between the VOUT pin and ground.

It may also be possible to use tantalum or film capacitors at the output, but these are not as attractive for

reasons of size and cost (see the section CAPACITOR CHARACTERISTICS).

NO-LOAD STABILITY

The LP3983 will remain stable and in regulation with no external load. This is specially important in CMOS RAM

keep-alive applications.

Copyright © 2004–2013, Texas Instruments Incorporated

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