WM8945ECSSLASHR datasheet(9/169 Pages) WOLFSON

9 / 169 page

Production Data

WM8945

PD, May 2011, Rev 4.1

THERMAL PERFORMANCE

Thermal analysis should be performed in the intended application to prevent the WM8945 from

exceeding maximum junction temperature. Several contributing factors affect thermal performance

most notably the physical properties of the mechanical enclosure, location of the device on the PCB

in relation to surrounding components and the number of PCB layers. Connecting the GND balls

through thermal vias and into a large ground plane will aid heat extraction.

Three main heat transfer paths exist to surrounding air as illustrated below in Figure 1:

Package top to air (radiation).

Package bottom to PCB (radiation).

Package balls to PCB (conduction).

Figure 1 Heat Transfer Paths

The temperature rise TR is given by TR = PD * ӨJA

PD is the power dissipated in the device.

ӨJA is the thermal resistance from the junction of the die to the ambient temperature

and is therefore a measure of heat transfer from the die to surrounding air. ӨJA is

determined with reference to JEDEC standard JESD51-9.

The junction temperature TJ is given by TJ = TA +TR, where TA is the ambient temperature.

PARAMETER

SYMBOL

MIN

TYP

MAX

UNIT

Operating temperature range

-40

°C

Operating junction temperature

-40

125

°C

Thermal Resistance

(Junction to Case)

ӨJC

°C/W

Thermal Resistance

(Junction to Ambient)

ӨJA

°C/W

Notes:

Junction temperature is a function of ambient temperature and of the device operating conditions. The ambient

temperature limits and junction temperature limits must both be observed.

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