RT8289
The maximum power dissipation depends on operating
ambient temperature for fixed TJ (MAX) and thermal
resistance θJA. For the RT8289, the Figure 5 of derating
curves allows the designer to see the effect of rising
ambient temperature on the maximum power dissipation
allowed.
(d) Copper Area = 50mm2 ,θJA = 51°C/W
2.2
Four Layer PCB
2.0
1.8
Copper Area
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2
70mm
2
50mm
30mm
2
2
10mm
Min.Layout
(e) Copper Area = 70mm2 ,θJA = 49°C/W
Figure 4. Themal Resistance vs. CopperArea Layout
Design
0
25
50
75
100
125
(°C)
Ambient Temperature
Layout Consideration
Figure 5.Derating Curves for RT8289 Package
Follow the PCB layout guidelines for optimal performance
of the RT8289.
` Keep the traces of the main current paths as short and
wide as possible.
` Put the input capacitor as close as possible to the device
pins (VINandGND).
` LX node is with high frequency voltage swing and should
be kept at small area. Keep analog components away
from the LX node to prevent stray capacitive noise pick-
up.
(a) Copper Area = (2.3 x 2.3) mm2,θJA = 75°C/W
` Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback
components near the RT8289.
` Connect all analog grounds to a command node and
then connect the command node to the power ground
behind the output capacitors.
(b) Copper Area = 10mm2,θJA = 64°C/W
` An example of PCB layout guide is shown in Figure 6 for
reference.
(c) Copper Area = 30mm2 ,θJA = 54°C/W
DS8289-01 March 2011
www.richtek.com
11
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
