LP5951

SNVS345F – JUNE 2006 – REVISED MAY 2013

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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.

given package can be calculated using the equation:

(1)

With a

The actual power dissipation across the device can be estimated by the following equation:

(2)

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

As is common with most regulators, the LP5951 requires external capacitors to ensure stable operation. The

LP5951 is specifically designed for portable applications requiring minimum board space and the smallest size

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

INPUT CAPACITOR

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

LP5951 input pin and ground (this capacitance value may be increased without limit).

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

analogue 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 ensured 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 remain

≥0.7µF over the entire operating temperature range.

OUTPUT CAPACITOR

The LP5951 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor

(dielectric types X7R, Z5U, or Y5V) in the 1.0µF range (up to 47µF) and with ESR between 3 m

Ω to 500 mΩ is

suitable in the LP5951 application circuit.

analogue ground.

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

(1)

In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may

part/package in the application (

8

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