Production Data
WM8352
4
THERMAL CHARACTERISTICS
Thermal analysis must be performed in the intended application to prevent the WM8352 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 nine central
GND balls through thermal vias and into a large ground plane will aid heat extraction.
Three main heat transfer paths exist to surrounding air:
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Package top to air (radiation).
Package bottom to PCB (radiation).
Package leads to PCB (conduction).
The temperature rise TR is given by TR = PD * ӨJA
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PD is the power dissipated by 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.
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For WM8352, ӨJA = 32°C/W
The junction temperature TJ is given by TJ = TA + TR
TA, is the ambient temperature.
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The worst case conditions are when the WM8352 is operating in a high ambient temperature, with
low supply voltage, high duty cycle and high output current. Under such conditions, it is possible that
the heat dissipated could exceed the maximum junction temperature of the device. Care must be
taken to avoid this situation. An example calculation of the junction temperature is given below.
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P = 1W (example figure)
D
Ө
= 32°C/W
JA
TR = PD * ӨJA = 32°C
= 85°C (example figure)
T
A
T = TA +TR = 117°C
J
The minimum and maximum operating junction temperatures for the WM8352 are quoted in
Section 5. The maximum junction temperature is 125°C. Therefore, the junction temperature in the
above example is within the operating limits of the WM8352.
PD, February 2011, Rev 4.4
13
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
