RT8258 RICHTEK [Richtek Technology Corporation], RT8258 Datasheet - Page 9

• Manufacturer Part Number: RT8258
• Description: 1.2A, 24V, 700kHz Step-Down Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

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 T
temperature, T
the junction to ambient thermal resistance.
For recommended operating conditions specification of the
RT8258, the maximum junction temperature of the die is
125°C. The junction to ambient thermal resistance θ
layout dependent. For T/SOT-23-6 package, the thermal
resistance θ
layer thermal test board. The maximum power dissipation
at T
P
T/SOT-23-6 package
The maximum power dissipation depends on operating
ambient temperature for fixed T
θ
allows the designer to see the effect of rising ambient
temperature on the maximum power dissipation allowed.
DS8258-02 March 2011
JA
D(MAX)
D(MAX)
. For RT8258 package, the Figure 3 of derating curve
A
= 25°C can be calculated by following formula :
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Figure 3. Derating Curve for RT8258 Package
= (T
= (125°C − 25°C) / (250°C/W) = 0.4W for
J(MAX)
0
J(MAX)
JA
is 250°C/W on standard JEDEC 51-3 single
A
is the ambient temperature and the θ
is the maximum operation junction
− T
25
Ambient Temperature (°C)
A
) / θ
JA
50
J(MAX)
T/SOT-23-6
and thermal resistance
75
Single Layer
100
PCB
JA
JA
125
is
is
Layout Consideration
Follow the PCB layout guidelines for optimal performance
of RT8258.
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).
PHASE node is with high frequency voltage swing and
should be kept at small area. Keep sensitive components
away from the PHASE node to prevent stray capacitive
noise pick-up.
Place the feedback components to the FB pin as close
as possible.
Connect the GND to a ground plane for noise reduction
and thermal dissipation.
V
OUT
R2
R1
Figure 4. PCB Layout Guide
BOOT
GND
FB
2
3
1
C
B
V
6
5
4
OUT
L
PHASE
VIN
EN
C
RT8258
OUT
www.richtek.com
D1
GND
C
IN
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