rt8010 Richtek Technology Corporation, rt8010 Datasheet - Page 12

• Manufacturer Part Number: rt8010
• Description: 1.5mhz, High Efficiency Step-down Dc/dc Converter
• Manufacturer: Richtek Technology Corporation

RT8010/A
2. I
internal switches, R
continuous mode, the average output current flowing
through inductor L is “chopped” between the main switch
and the synchronous switch. Thus, the series resistance
looking into the LX pin is a function of both top and bottom
MOSFET R
R
The R
obtained from the Typical Performance Characteristics
curves. Thus, to obtain I
and multiply the result by the square of the average output
current.
Other losses including C
losses and inductor core losses generally account for less
than 2% of the total loss.
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 T
temperature, T
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT8010/A DC/DC converter, where T
junction temperature of the die and T
ambient temperature. The junction to ambient thermal
resistance θ
packages, the thermal resistance θ
standard JEDEC 51-7 four layers thermal test board.
The maximum power dissipation at T
calculated by following formula :
P
WDFN-6L 2x2 packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance θ
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12
D(MAX)
SW
D(MAX)
2
R losses are calculated from the resistances of the
= R
DS(ON)
= ( T
DS(ON)TOP
= (125°C − 25°C) / 165°C/W = 0.606W for
J(MAX)
DS(ON)
for both the top and bottom MOSFETs can be
J(MAX)
JA
JA
.
A
is layout dependent. For WDFN-6L 2x2
is the ambient temperature and the θ
is the maximum operation junction
x DC + R
and the duty cycle (DC) as follows :
- T
A
SW
) / θ
2
R losses, simply add R
and external inductor R
JA
IN
DS(ON)BOT
and C
OUT
JA
J(MAX)
J(MAX)
x (1−DC)
is 165°C/W on the
A
A
ESR dissipative
is the maximum
= 25°C can be
is the maximum
and thermal
SW
to R
L
JA
. In
is
L
For RT8010/A packages, the Figure 5 of derating curves
allows the designer to see the effect of rising ambient
temperature on the maximum power allowed.
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
resistance of C
discharge C
by the regulator to return V
During this recovery time, V
overshoot or ringing that would indicate a stability problem.
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of RT8010/A.
LX node is with high frequency voltage swing and should
Connect feedback network behind the output capacitors.
Put the input capacitor as close as possible to the device
For the main current paths as indicated in bold lines in
Figure 6, keep their traces short and wide.
pins (VIN and GND).
be kept small area. Keep analog components away from
LX node to prevent stray capacitive noise pick-up.
Keep the loop area small. Place the feedback
components near the RT8010/A.
Figure 5. Derating Curves for RT8010/A Package
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
WDFN-6L 2x2
LOAD
OUT
(ESR), where ESR is the effective series
generating a feedback error signal used
OUT
25
. ΔI
OUT
Ambient Temperature
LOAD
immediately shifts by an amount
50
OUT
also begins to charge or
WQFN-16L 3x3
OUT
DS8010/A-02 March 2007
to its steady-state value.
can be monitored for
75
Four Layers PCB
(°C)
100
125