RT8253B RICHTEK [Richtek Technology Corporation], RT8253B Datasheet - Page 12

• Manufacturer Part Number: RT8253B
• Description: 3A, 23V, 1.2MHz Synchronous Step-Down Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8253B
Thermal Considerations
For continuous operation, do not exceed the maximum
operation junction temperature 125°C. 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
temperature ,
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT8253B, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance
dependent. For PSOP-8 package, the thermal resistance
θ
thermal test board. The maximum power dissipation at
T
P
(min.copper area PCB layout)
P
(70mm
The thermal resistance
determined by the package architecture design and the
PCB layout design. However, the package architecture
design had been designed. If possible, it's useful to
increase thermal performance by the PCB layout copper
design. The thermal resistance
adding copper area under the exposed pad of SOP-8
(Exposed Pad) package.
www.richtek.com
12
JA
A
D(MAX)
D(MAX)
D(MAX)
= 25°C
is 75°C/W on the standard JEDEC 51-7 four-layer
2
= (T
copper area PCB layout)
T
=
J(MAX)
=
can be calculated by following formula :
J(MAX)
(125°C
(125°C
Chip Enable
T
4.5V to 23V
A
is the maximum operation junction
is the ambient temperature and the
− T
* : Optional
V
A
− 25°C) / (75°C/W) = 1.333W
− 25°C) / (49°C/W) = 2.04W
IN
) / θ
θ
Figure 5. Reference Circuit with Snubber and Enable Timing Control
JA
JA
C
0.1µF
R
SS
C
of SOP-8 (Exposed Pad) is
EN
EN
*
*
θ
Exposed Pad(9)
JA
can be decreased by
10µF x 2
C
IN
4,
2
7
8
θ
VIN
EN
SS
GND
JA
is layout
RT8253B
θ
JA
COMP
BOOT
is
SW
FB
6
1
3
5
As shown in Figure 6, the amount of copper area to which
the SOP-8 (Exposed Pad) is mounted affects thermal
performance. When mounted to the standard
SOP-8 (Exposed Pad) pad (Figure 6.a), θ
Adding copper area of pad under the SOP-8 (Exposed
Pad) (Figure 6.b) reduces the θ
increasing the copper area of pad to 70mm
reduces the θ
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
dissipation allowed.
R
BOOT
Figure 7. Derating Curves for RT8253B Package
R
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
C
S
S
*
*
*
2.2nF
0
C
C
C
100nF
C
NC
BOOT
JA
P
22k
JA
R
. For RT8253B packages, the Figure 7 of
C
25
to 49°C/W.
3.6µH
L
Ambient Temperature (°C)
75k
R1
R2
24k
50
JA
DS8253B-02 March 2011
C
22µFx2
to 64°C/W. Even further,
OUT
75
J(MAX)
V
3.3V/3A
OUT
maximum power
Four-Layer PCB
Copper Area
70mm
50mm
30mm
10mm
and thermal
JA
2
Min.Layout
100
(Figure 6.e)
is 75°C/W.
2
2
2
2
125