7 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

7.1 Application Information

7.1.1 Estimating Junction Temperature

The JEDEC standard now recommends the use of psi (Ψ) thermal metrics to estimate the junction temperatures

of the linear regulator when in-circuit on a typical PCB board application. These metrics are not thermal

resistance parameters and instead offer a practical and relative way to estimate junction temperature. These

psi metrics are determined to be significantly independent of the copper area available for heat-spreading.

The Thermal Information lists the primary thermal metrics, which are the junction-to-top characterization

parameter (ψJT) and junction-to-board characterization parameter (ψJB). These parameters provide two methods

for calculating the junction temperature (TJ), as described in the following equations. Use the junction-to-top

characterization parameter (ψJT) with the temperature at the center-top of device package (TT) to calculate

the junction temperature. Use the junction-to-board characterization parameter (ψJB) with the PCB surface

temperature 1mm from the device package (TB) to calculate the junction temperature.

TJ = TT + ψJT × PD

(2)

where:

• PD is the dissipated power

• TT is the temperature at the center-top of the device package

TJ = TB + ψJB × PD

(3)

where:

• TB is the PCB surface temperature measured 1mm from the device package and centered on the package

edge

For detailed information on the thermal metrics and how to use them, see the Semiconductor and IC Package

Thermal Metrics application note.

7.1.2 Input and Output Capacitor Requirements

Although an input capacitor is not required for stability, good analog design practice is to connect a capacitor

from IN to GND. This capacitor counteracts reactive input sources and improves transient response, input ripple,

and PSRR. Use an input capacitor if the source impedance is more than 0.5Ω. A higher value capacitor can be

necessary if large, fast rise-time load or line transients are anticipated or if the device is located several inches

from the input power source.

Dynamic performance of the device is improved with the use of an output capacitor. Use an output capacitor

within the range specified in the Recommended Operating Conditions table for stability.

7.1.3 Noise Bypass Capacitor (CBYPASS)

The LP2992 allows for low-noise performance with the use of a bypass capacitor that is connected to the internal

band-gap reference with the BYPASS pin. This high-impedance band-gap circuitry is biased in the microampere

range and, thus, cannot be loaded significantly, otherwise, the output (and, correspondingly, the output of the

regulator) changes. Thus, for best output accuracy, dc leakage current through CBYPASS must be minimized as

LP2992

SNVS171L – NOVEMBER 2001 – REVISED FEBRUARY 2025

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