Production Data
WM8945
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
-40
-40
TYP
MAX
85
UNIT
°C
Operating temperature range
Operating junction temperature
Thermal Resistance
(Junction to Case)
TA
TJ
125
°C
ӨJC
30
60
°C/W
Thermal Resistance
(Junction to Ambient)
ӨJA
°C/W
Notes:
1. 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.
PD, May 2011, Rev 4.1
9
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
