RT4533/A
Where TJ(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJAis
the junction to ambient thermal resistance.
Layout Consideration
For best performance of the RT4533/A, the following guide
lines must be strictly followed.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
TSOT-23-6 package, the thermal resistance, θJA, is
197.4°C/W on the standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by following formula :
Input and Output capacitors should be placed close to
the IC and connected to ground plane to reduce noise
coupling.
The GND and Exposed Pad should be connected to a
strong ground plane for heat sinking and noise protection.
Keep the main current traces as possible as short and
wide.
PD(MAX) = (125°C − 25°C) / (197.4°C/W) = 0.5W for
LX node of DC/DC converter is with high frequency
TSOT-23-6 package
voltage swing. It should be kept at a small area.
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. The derating curve in Figure 1 of derating
curves allows the designer to see the effect of rising
ambient temperature on the maximum power allowed.
Place the feedback components as close as possible
to the IC and keep away from the noisy devices.
0.6
Four-Layer PCB
0.5
0.4
0.3
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum PowerDissipation
Copyright 2015 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS4533/A-02 September 2015
www.richtek.com
9
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