RT9912A RICHTEK [Richtek Technology Corporation], RT9912A Datasheet - Page 12

• Manufacturer Part Number: RT9912A
• Description: Multi-Channel Power Management IC for Portable Device
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9912A
For buck converter, calculate the minimum output
capacitance as the following formula :
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 125°C, T
θ
For recommended operating conditions specification of
RT9912A, where T
temperature of the die (125°C) and T
ambient temperature. The junction to ambient thermal
resistance θ
packages, the thermal resistance θ
standard JEDEC 51-7 four layers thermal test board. The
maximum power dissipation at T
by following formula :
P
WQFN-24L 4x4 packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance θ
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
www.richtek.com
12
JA
D(MAX)
D(MAX)
C
is the junction to ambient thermal resistance.
OUT
= (T
= (125°C − 25°C) / (54°C/W) = 1.852W for
≥
J(MAX)
J(MAX)
I
JA
JA
OUT(MAX)
. For RT9912A packages, the Figure 2 of
is layout dependent. For WQFN-24L 4x4
is the maximum operation junction
− T
f V
×
A
A
J(MAX)
) / θ
×
is the ambient temperature and the
REPPLE_C
⎛
⎜
⎝
1
JA
−
I
OUT(MAX)
is the maximum junction
I
PEAK
A
= 25°C can be calculated
JA
J(MAX)
⎞
⎟
⎠
A
is 54° C/W on the
2
is the maximum
and thermal
Layout Considerations
For the best performance of the RT9912A, the following
PCB Layout guidelines must be strictly followed.
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 possible as wide and
short.
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.
Figure 2. Derating Curves for RT9912A Packages
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
Ambient Temperature (°C)
50
WQFN-24L 4x4
DS9912A-01 April 2011
75
Four Layers PCB
100
125