LP5910 datasheet(16/31 Pages) TI

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8.2.2.9 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 4 or Equation 5.

TJ(MAX) = TTOP + (ΨJT × PD(MAX))

(4)

where

• PD(MAX) is explained in Equation 1.

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

TJ(MAX) = TBOARD + (ΨJB × PD(MAX))

(5)

where

• PD(MAX) is explained in Equation 1.

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

package edge.

For more information about the thermal characteristics ΨJT and ΨJB, see the Semiconductor and IC Package

Thermal Metrics application report, available for download at www.ti.com.

For more information about measuring TTOP and TBOARD, see the Using New Thermal Metrics application report,

available for download at www.ti.com.

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

Characteristics of Linear and Logic Packages Using JEDEC PCB Designs application report, available for

download at www.ti.com.

8.2.3 Application Curves

Time (µs)

-25

100

125

150

0.5

1.5

2.5

D021

VIN

VOUT

VEN = VIN

VOUT = 1.8 V

COUT = 1 µF

Figure 8-2. Turnon Time

Time (µs)

-20

-10

-12

-8

-4

100

120

D022

IOUT

'VOUT

VIN = 2.3 V

VOUT = 1.8 V

COUT = 1 µF

IOUT = 1 mA to 100 mA

tRISE = 10 µs

Figure 8-3. Load Transient Response

LP5910

SNVSA91F – SEPTEMBER 2015 – REVISED APRIL 2021

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