RT9008 데이터 시트보기 (PDF) - Richtek Technology
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RT9008 Datasheet PDF : 9 Pages
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RT9008
Where TJ(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient resistance.
For recommended operating conditions specification of
the RT9008, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance θJA for SOT-
23-6 package is 250°C/W on the standard JEDEC 51-3
single-layer thermal test board.
The maximum allowed power dissipation at TA = 25°C can
be calculated by following formula :
For SOT-23-6 package,
PD(MAX) = (125°C − 25°C)/(250°C/W) = 0.400 W
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. For RT9008 package, the Figure 3 of
derating curve allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation allowed.
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
Single Layer PCB
SOT-23-6
25
50
75
100
125
Ambient Temperature (°C)
Figure 3. Derating Curves for RT9008 Package
Layout Considerations
There are three critical layout considerations. One is the
divider resistors should be located as close to the RT9008
FB pin as possible to minimize noise
The second is the placement of capacitors. The CIN and
COUT have to be placed near the N-MOSFET for improving
performance.
The third is the copper area for pass element, it should be
as large as possible when the pass element operating
under high power situation that could rise the junction
temperature. Considering the package thermal resistance
limitation, the copper area should be large enough to
handle the power dissipation shown as Figure 4.
VIN
CIN
DRI
COUT
VCC
CCC
GND
VCC DRI SS
6
5
4
2
3
EN GND FB
R1
R2
VOUT
Figure 4. PCB Layout Guide
GND
www.richtek.com
8
DS9008-01 April 2011
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