RT9712 RICHTEK [Richtek Technology Corporation], RT9712 Datasheet - Page 12

• Manufacturer Part Number: RT9712
• Description: 90m?, 1A/1.5A High-Side Dual Power Switches with Flag
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9712
Power Dissipation
The junction temperature of the RT9712 series depend
on several factors such as the load, PCB layout, ambient
temperature and package type. The output pin of
RT9712A/B/C/D can deliver the current of up to 1.5A
(RT9712A/B), and 0.6A (RT9712C/D) respectively over the
full operating junction temperature range. However, the
maximum output current must be derated at higher
ambient temperature to ensure the junction temperature
does not exceed 100°C. With all possible conditions, the
junction temperature must be within the range specified
under operating conditions. Power dissipation can be
calculated based on the output current and the R
switch as below.
P
Although the devices are rated for 1.5A and 0.6A of output
current, but the application may limit the amount of output
current based on the total power dissipation and the
ambient temperature.
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 100°C, T
the θ
For recommended operating conditions specification,
where T
die (100°C) and T
The junction to ambient thermal resistance θ
dependent. For SOP-8 and MSOP-8 packages, the thermal
resistance θ
dissipation at T
formula :
P
SOP-8 and MSOP-8 packages
Copyright
www.richtek.com
12
D
D(MAX)
D(MAX)
= R
JA
DS(ON)
©
= ( T
is the junction to ambient thermal resistance.
J(MAX)
= (100°C − 25°C) / (160°C/W) = 0.469W for
2012 Richtek Technology Corporation. All rights reserved.
J(MAX)
J(MAX)
x I
is the maximum junction temperature of the
JA
OUT
A
is the maximum operation junction
is 160°C/W. The maximum power
A
= 25°C can be calculated by following
− T
is the maximum ambient temperature.
2
A
A
) / θ
is the ambient temperature and
JA
JA
is layout
DS(ON)
of
The maximum power dissipation depends on the operating
ambient temperature for fixed T
resistance, θ
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Layout Consideration
For best performance of the RT9712 series, the following
guidelines must be strictly followed.
Figure 3. Derating Curve of Maximum Power Dissipation
Input and output capacitors should be placed close to
the IC and connected to ground plane to reduce noise
coupling.
The GND should be connected to a strong ground plane
for heat sink.
Keep the main current traces as possible as short and
wide.
is a registered trademark of Richtek Technology Corporation.
0.5
0.4
0.3
0.2
0.1
C
0
IN
0
GND
The main current trace should be as
possible as short and wide.
The input and output capacitors should
be placed as close as possible to the IC.
10
JA
GND
Figure 4. PCB Layout Guide
VIN
. The derating curve in Figure 3 allows the
20
Ambient Temperature (°C)
30
2
3
4
40
DS9712-04 November 2012
8
7
6
5
50
SOP-8/MSOP-8
60
VOUT1
VOUT2
J(MAX)
Single
70
and thermal
80
C
C
OUT2
OUT1
Layers
90
100