RT8270 RICHTEK [Richtek Technology Corporation], RT8270 Datasheet - Page 10

• Manufacturer Part Number: RT8270
• Description: 2A, 22V, 1.2MHz Step-Down Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8270
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
discharge C
regulator to return V
this recovery time, V
ringing that would indicate a stability problem.
Thermal Considerations
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
RT8270, the maximum junction temperature is
junction to ambient thermal resistance
package is 120°C/W on the standard JEDEC 51-7 four-
layers thermal test board. The maximum power dissipation
at
P
SOP-8 packages
The maximum power dissipation depends on operating
ambient temperature for fixed
resistance
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
www.richtek.com
10
D(MAX)
D(MAX)
T
A
=
25°C
= ( T
=
T
J(MAX)
(125°C −
θ
LOAD
OUT
J(MAX)
JA
can be calculated by following formula :
T
. For RT8270 packages, the Figure 3 of
A
generating a feedback error signal for the
is the ambient temperature and the
is the maximum operation junction
(ESR) and also begins to charge or
− T
OUT
OUT
OUT
25°C) / (120°C/W) = 0.833W for
A
) / θ
can be monitored for overshoot or
to its steady-state value. During
immediately shifts by an amount
JA
T
J(MAX)
θ
and thermal
JA
125°C.
for SOP-8
θ
The
JA
is
Layout Consideration
Follow the PCB layout guidelines for optimal performance
of the RT8270.
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 sensitive components away
from the LX node to prevent stray capacitive noise pick-
up.
Place the feedback components to the FB pin as close
as possible.
The GND and Exposed Pad should be connected to a
strong ground plane for heat sinking and noise protection.
Figure 3. Derating Curves for RT8270 Packages
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
25
Ambient Temperature (°C)
50
DS8270-01 March 2011
SOP-8
75
Four Layer PCB
100
125