3.3V

4.3V

IL =

300mA

500 Ps/DIV

VOUT

IOUT

IL =

300mA

500 Ps/DIV

RTJA

(160 - TA)

(0.300 x VD)

16

LP3982

SNVS185F – FEBRUARY 2002 – REVISED APRIL 2017

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Product Folder Links: LP3982

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Copyright © 2002–2017, Texas Instruments Incorporated

(12)

8.2.2.8 Estimating Junction Temperature

The EIA/JEDEC standard recommends the use of psi (Ψ) thermal characteristics to estimate the junction

temperatures of surface mount devices on a typical PCB board application. These characteristics are not true

thermal resistance values, but rather package specific thermal characteristics that offer practical and relative

means of estimating junction temperatures. These psi metrics are determined to be significantly independent of

copper-spreading area. The key thermal characteristics (ΨJT and ΨJB) are given in Thermal Information and are

used in accordance with Equation 13 or Equation 14.

TJ(MAX) = TTOP + (ΨJT × PD(MAX))

where

•

PD(MAX) is explained in Equation 9.

•

TTOP is the temperature measured at the center-top of the device package.

(13)

TJ(MAX) = TBOARD + (ΨJB × PD(MAX))

where

•

PD(MAX) is explained in Equation 9.

•

TBOARD is the PCB surface temperature measured 1-mm from the device package and centered on the

package edge.

(14)

For more information about the thermal characteristics ΨJT and ΨJB, see the TI Application Report Semiconductor

and IC Package Thermal Metrics (SPRA953), available for download at www.ti.com.

For more information about measuring TTOP and TBOARD, see the TI Application Report Using New Thermal

Metrics (SBVA025), available for download at www.ti.com.

For more information about the EIA/JEDEC JESD51 PCB used for validating RθJA, see the TI Application Report

Thermal Characteristics of Linear and Logic Packages Using JEDEC PCB Designs (SZZA017), available for

download at www.ti.com.

8.2.3 Application Curves

Figure 19. Line Transient Response

Figure 20. Load Transient

9 Power Supply Recommendations

The LP3982 is designed to operate from an input voltage supply range between 2.5 V and 6 V. The input voltage

range provides adequate headroom in order for the device to have a regulated output. This input supply must be

well regulated. If the input supply is noisy, additional input capacitors with low ESR can help to improve the

output noise performance.