DS9535A Datasheet, PDF (16/18 Pages) Richtek Technology Corporation – High Efficiency Switching Mode Battery Charge

RT9535A
where TJ(MAX) is the maximum junction temperature,
TA is the ambient temperature, and JA is the junction to
ambient thermal resistance.
For recommended operating condition specifications,
the maximum junction temperature is 125C. The
junction to ambient thermal resistance, JA, is layout
dependent. For WQFN-16L 4x4 package, the thermal
resistance, JA, is 28.5C/W on a standard JEDEC
51-7 four-layer thermal test board. The maximum
power dissipation at TA = 25C can be calculated by
the following formula :
PD(MAX) = (125C  25C) / (28.5C/W) = 3.5W for
WQFN-16L 4x4 package
The maximum power dissipation depends on the
operating ambient temperature for fixed TJ(MAX) and
thermal resistance, JA. The derating curve in Figure 1
allows the designer to see the effect of rising ambient
temperature on the maximum power dissipation.
5.0
Four-Layer PCB
4.0
3.0
2.0
1.0
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum Power
Dissipation
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DS9535A-04 February 2016