RT8272 RICHTEK [Richtek Technology Corporation], RT8272 Datasheet - Page 10

• Manufacturer Part Number: RT8272
• Description: 3A, 24V, 1.2MHz Step-Down Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8272
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V
equal to ΔI
C
to return V
time, V
would indicate a stability problem.
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
RT8272, where the maximum junction temperature is
125°C. The junction to ambient thermal resistance θ
layout dependent. For SOP-8 (Exposed Pad) packages,
the thermal resistance θ
JEDEC 51-7 four-layers thermal test board. The maximum
power dissipation at T
following formula:
P
SOP-8 (Exposed Pad) packages
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 maximum power
allowed.
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10
D(MAX)
D(MAX)
OUT
generating a feedback error signal for the regulator
OUT
= ( T
= (125°C − 25°C) / (75°C/W) = 1.333W for
OUT
J(MAX)
LOAD
can be monitored for overshoot or ringing that
J(MAX)
JA
to its steady-state value. During this recovery
. For RT8272 packages, the Figure 3 of
A
(ESR) also begins to charge or discharge
is the ambient temperature and the θ
is the maximum operation junction
- T
OUT
A
) / θ
A
immediately shifts by an amount
JA
= 25°C can be calculated by
JA
is 75°C/W on the standard
J(MAX)
and thermal
JA
JA
is
is
Layout Consideration
Follow the PCB layout guidelines for optimal performance
of RT8272.
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).
LX node is with high frequency voltage swing and should
be kept at small area. Keep analog components away
from the LX node to prevent stray capacitive noise pick-
up.
Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback
components near the RT8272.
Connect all analog grounds to a command node and
then connect the command node to the power ground
behind the output capacitors.
An example of PCB layout guide is shown in Figure 4
for reference.
Figure 3. Derating Curves for RT8272 Packages
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
Ambient Temperature
50
DS8272-02 March 2011
75
Four Layer PCB
(°C)
100
125