rt8070 Richtek Technology Corporation, rt8070 Datasheet - Page 10

• Manufacturer Part Number: rt8070
• Description: 4a, 2mhz, Synchronous Step-down Converter
• Manufacturer: Richtek Technology Corporation

RT8070
four-layer thermal test board. The maximum power
dissipation at T
formulas :
P
SOP-8 (Exposed Pad) package
P
WDFN-8L 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T
resistance, θ
curves in Figure 3 allow the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
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10
D(MAX)
D(MAX)
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Figure 3. Derating Curves for RT8070 Package
= (125°C − 25°C) / (75°C/W) = 1.333W for
= (125°C − 25°C) / (70°C/W) = 1.429W for
0
JA
A
. For the RT8070 package, the derating
SOP-8 (Exposed Pad)
= 25°C can be calculated by the following
25
Ambient Temperature (°C)
50
WDFN-8L 3x3
75
J(MAX)
Four Layer PCB
and thermal
100
125
C
COMP
C
C
COMP
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of the IC.
SS
C
GND
Place the compensation
components as close to
the IC as possible
SS
Connect the terminal of the input capacitor(s), C
close to the VIN pin as possible. This capacitor provides
the AC current into the internal power MOSFETs.
LX node experiences high frequency voltage swings so
should be kept within a small area.
Keep all sensitive small signal nodes away from the LX
node to prevent stray capacitive noise pick up.
Connect the FB pin directly to the feedback resistors.
The resistive voltage divider must be connected between
V
GND
Place the compensation
components as close to
the IC as possible
OUT
R
COMP
R
COMP
V
and GND.
Place the input and output capacitors
as close to the IC as possible
IN
V
(a) For SOP-8 (Exposed Pad) package
Place the input and output capacitors
as close to the IC as possible
IN
COMP
C
IN
C
VIN
SS
EN
IN
(b) For WDFN-8L 3x3 package
GND
Figure 4. PCB Layout Guide
COMP
GND
VIN
EN
SS
2
3
4
1
2
3
4
GND
9
9
8
7
6
5
C
8
7
6
5
OUT
C
PGOOD
FB
RT
LX
OUT
PGOOD
FB
RT
LX
DS8070-03 March 2011
V
OUT
V
OUT
Place the feedback
resistors as close to
the IC as possible
L1
Place the feedback
resistors as close to
the IC as possible
L1
R2
LX should be connected
to inductor by wide and
short trace, and keep
sensitive components
away from this trace
R
R2
R1
R
LX should be connected
to inductor by wide and
short trace, and keep
sensitive components
away from this trace
OSC
R1
OSC
V
GND
V
OUT
GND
OUT
IN
, as