RT8205A RICHTEK [Richtek Technology Corporation], RT8205A Datasheet - Page 26

• Manufacturer Part Number: RT8205A
• Description: High Efficiency, Main Power Supply Controllers for Notebook Computers
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8205A/B/C
test board. The maximum power dissipation at T
can be calculated by following formula :
P
WQFN-24L 4x4 packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance θ
designer to see the effect of rising ambient temperature
on the maximum power allowed.
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www.richtek.com
26
Figure 7. Derating Curve of Maximum Power Dissipation
D(MAX)
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
©
= (125°C − 25°C) / (52°C/W) = 1.923W for
2012 Richtek Technology Corporation. All rights reserved.
0
JA
. The Figure 7 of derating curves allows the
25
Ambient Temperature (°C)
50
WQFN-24L 4x4
75
J(MAX)
Four Layers PCB
and thermal
100
A
= 25°C
125
Layout Considerations
Layout is very important in high frequency switching
converter design. If the IC is designed improperly, the PCB
could radiate excessive noise and contribute to the
converter instability. Certain points must be considered
before starting a layout using the RT8205A/B/C.
Place the filter capacitor close to the IC, within 12 mm
(0.5 inch) if possible.
Keep current limit setting network as close as possible
to the IC. Routing of the network should avoid coupling
to high-voltage switching node.
Connections from the drivers to the respective gate of
the high-side or the low-side MOSFET should be as
short as possible to reduce stray inductance. Use 0.65-
mm (25 mils) or wider trace.
All sensitive analog traces and components such as
VOUTx, FBx, GND, ENTRIPx, PGOOD, and TONSEL
should be placed away from high-voltage switching
nodes such as PHASEx, LGATEx, UGATEx, or BOOTx
nodes to avoid coupling. Use internal layer(s) as ground
plane(s) and shield the feedback trace from power traces
and components.
Gather ground terminal of VIN capacitor(s), VOUTx
capacitor(s), and source of low-side MOSFETs as close
as possible. PCB trace defined as PHASEx node, which
connects to source of high-side MOSFET, drain of low-
side MOSFET and high-voltage side of the inductor,
should be as short and wide as possible.
is a registered trademark of Richtek Technology Corporation.
DS8205A/B/C-06 July 2012