RT9953 RICHTEK [Richtek Technology Corporation], RT9953 Datasheet - Page 16

• Manufacturer Part Number: RT9953
• Description: 4+1 CH Power Management IC
• Manufacturer: RICHTEK [Richtek Technology Corporation]

www.richtek.com
16
RT9953
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
following formula :
P
Where T
temperature, T
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT9953, the maximum junction temperature is 125 C. The
junction to ambient thermal resistance
dependent. For WQFN-24L 4x4 package, the thermal
resistance
four layers thermal test board. The maximum power
dissipation at T
formula :
P
WQFN-24L 4x4
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance
derating curve allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation allowed.
D(MAX)
D(MAX)
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Figure 1. Derating Curves for RT9953 Package
= (T
= (125 C
0
J(MAX)
J(MAX)
JA
JA
. For RT9953 package, the Figure 1 of
A
is 54 C/W on the standard JEDEC 51-7
A
is the ambient temperature and the
is the maximum operation junction
= 25 C can be calculated by following
25
Ambient Temperature (°C)
T
A
25 C) / (54 C/W) = 1.852W for
) /
JA
50
WQFN-24L 4x4
75
J(MAX)
Four Layers PCB
and thermal
100
JA
is layout
125
JA
is
Layout Considerations
For the best performance of the RT9953, the following
PCB layout guidelines must be strictly followed :
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Place the input and output capacitors as close as
possible to the input and output pins respectively for
good filtering.
Keep the main power traces as wide and short as
possible.
The switching node area connected to LX and inductor
should be minimized for lower EMI.
Place the feedback components as close as possible
to the FB pin and keep these components away from
the noisy devices.
Connect the GND and Exposed Pad to a strong ground
plane for maximum thermal dissipation and noise
protection.
CH5 PCB trace and component had put different PCB
side to avoid LX3 and LX4 switching noise.
DS9953-02 April 2011