rt8287a Richtek Technology Corporation, rt8287a Datasheet - Page 12

• Manufacturer Part Number: rt8287a
• Description: 4a, 21v 500khz Synchronous Step-down Converter
• Manufacturer: Richtek Technology Corporation

RT8287A
It is strongly recommended to reserve the R-C snubber
during PCB layout for EMI improvement. Moreover,
reducing the SW trace area and keeping the main power
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
P
where T
the ambient temperature, and
thermal resistance.
For recommended operating condition specifications of
the RT8287A, the maximum junction temperature is 125 C
and T
thermal resistance,
14L 4x3 package, the thermal resistance,
on a standard JEDEC 51-7 four-layer thermal test board.
The maximum power dissipation at T
calculated by the following formula :
P
WDFN-14L 4x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T
resistance,
curve in Figure 6 allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
www.richtek.com
12
D(MAX)
D(MAX)
A
is the ambient temperature. The junction to ambient
= (T
J(MAX)
= (125 C
J(MAX)
PGOOD
JA
is the maximum junction temperature, T
. For the RT8287A package, the derating
V
IN
T
A
JA
25 C) / (60 C/W) = 1.667W for
) /
* : Optional
, is layout dependent. For WDFN-
Figure 5. Reference Circuit with Snubber and Enable Timing Control
JA
R
C
EN
EN
*
*
JA
100k
is the junction to ambient
R3
C
C
C
J(MAX)
IN
A
11
= 25 C can be
1
7
9
JA
and thermal
VIN
PGOOD
VCC
EN
, is 60 C/W
AGND
RT8287A
14
GND
A
BOOT
12, 13, 15 (Exposed Pad)
is
SW
SS
FB
6
2, 3, 4, 5
8
10
in a small loop will be helpful on EMI performance. For
detailed PCB layout guide, please refer to the section
Layout Considerations.
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of the IC.
}
}
}
Keep the traces of the main current paths as short and
wide as possible.
Put the input capacitor as close as possible to the device
pins (VIN and GND).
SW node is with high frequency voltage swing and should
be kept at small area. Keep analog components away
from the SW node to prevent stray capacitive noise
pickup.
47nF
C
1.80
1.65
1.50
1.35
1.20
1.05
0.90
0.75
0.60
0.45
0.30
0.15
0.00
Figure 6. Derating Curve for RT8287A Package
SS
0
R
C
C
S
BOOT
S
*
*
R
T
25
L
Ambient Temperature (°C)
R1
R2
50
DS8287A-01 August 2011
C
75
OUT
V
Four-Layer PCB
OUT
100
125