RT6239A/B
Thermal Considerations
Layout Consideration
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
Follow the PCB layout guidelines for optimal
performance of the device.
Keep the traces of the main current paths as short and
wide as possible.
Put the input capacitor as close as possible to VIN and
VIN pins.
SW node is with high frequency voltage swing and
should be kept at small area. Keep analog components
away from the SW node to prevent stray capacitive noise
pickup.
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback
components near the device.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
UQFN-14L 2x3 (FC) package, the thermal resistance, θJA,
is 47.5°C/W on a standard four-layer thermal test board.
The maximum power dissipation at TA = 25°C can be
calculated by the following formula :
Connect all analog grounds to common node and then
connect the common node to the power ground behind
the output capacitors.
An example of PCB layout guide is shown in Figure 8
and Figure 9 for reference.
PD(MAX) = (125°C − 25°C) / (47.5°C/W) = 2.1W for
UQFN-14L 2x3 (FC) package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curve in Figure 7 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
2.4
Four-Layer PCB
2.0
1.6
1.2
0.8
0.4
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 7.Derating Curve of Maximum PowerDissipation
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18
DS6239A/B-04 May 2016
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
