rt8010b Richtek Technology Corporation, rt8010b Datasheet - Page 10

• Manufacturer Part Number: rt8010b
• Description: 1.5mhz, 800ma, High Efficiency Step-down Dc/dc Converter
• Manufacturer: Richtek Technology Corporation

RT8010B
In 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
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 125°C, T
θ
For recommended operating conditions specification of
RT8010B, where T
temperature of the die (125°C) and T
ambient temperature. The junction to ambient thermal
resistance
packages, the thermal resistance
standard JEDEC 51-7 four layers thermal test board. The
maximum power dissipation at T
by following formula :
P
WDFN-8L 2x2 packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance
www.richtek.com
10
JA
D(MAX)
D(MAX)
SW
is the junction to ambient thermal resistance.
= R
DS(ON)
= ( T
= (
DS(ON)TOP
J(MAX)
θ
θ
DS(ON)
for both the top and bottom MOSFETs can be
125°C
J(MAX)
JA
JA
.
is layout dependent. For WDFN-8L 2x2
is the maximum operation junction
x DC + R
and the duty cycle (DC) as follows :
−
−
T
A
A
J(MAX)
25°C
is the ambient temperature and the
) / θ
2
R losses, simply add R
IN
JA
DS(ON)BOT
) / (165°C/W) = 0.606W for
is the maximum junction
and C
A
=
25°C
θ
OUT
JA
J(MAX)
x (1−DC)
is 165°C/W on the
A
can be calculated
ESR dissipative
is the maximum
and thermal
SW
Preliminary
to R
L
For RT8010B 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 RT8010B.
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
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 RT8010B.
Connect all analog grounds to a command node and
then connect the command node to the power ground
behind the output capacitors.
Figure 5. Derating Curves for RT8010B Package
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
LOAD
OUT
(ESR), where ESR is the effective series
generating a feedback error signal used
OUT
25
Ambient Temperature (°C)
. ΔI
OUT
LOAD
immediately shifts by an amount
50
OUT
also begins to charge or
WDFN-8L 2x2
OUT
to its steady-state value.
DS8010B-00 July 2007
can be monitored for
75
Four Layers PCB
(°C)
100
125