RT9511 RICHTEK [Richtek Technology Corporation], RT9511 Datasheet - Page 21

• Manufacturer Part Number: RT9511
• Description: Fully Integrated Battery Charger with Two Step-Down Converters
• Manufacturer: RICHTEK [Richtek Technology Corporation]

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.
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 I
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.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. 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
For recommended operating conditions specification of
the RT9511, the maximum junction temperature is 125 C.
The junction to ambient thermal resistance
dependent. For WQFN-24L 4x4 packages, the thermal
DS9511-01 April 2011
JA
D(MAX)
SW
is the junction to ambient thermal resistance.
= R
DS(ON)
= ( T
DS(ON)TOP
J(MAX)
LOAD
DS(ON)
for both the top and bottom MOSFETs can be
OUT
J(MAX)
(ESR), where ESR is the effective series
generating a feedback error signal used
OUT
is the maximum operation junction
x DC + R
and the duty cycle (DC) as follows :
T
.
OUT
A
A
is the ambient temperature and the
) /
I
LOAD
2
immediately shifts by an amount
R losses, simply add R
IN
JA
DS(ON)BOT
OUT
and C
also begins to charge or
OUT
to its steady-state value.
can be monitored for
OUT
x (1-DC)
ESR dissipative
JA
is layout
SW
to R
L
resistance
four layers thermal test board. The maximum power
dissipation at T
formula :
P
WQFN-24L 4x4 packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance
derating curves allows designers to see the effect of rising
ambient temperature on the maximum power dissipation
allowed.
Layout Consideration
The RT9511 is a fully integrated solution for portable
applications including a single-cell Li- Ion battery charger
and two ideal high-efficiency step-down DC-DC converters
ideal. Careful PCB layout is necessary. For best
performance of the RT9511, the following guidelines should
be strictly followed.
}
}
}
D(MAX)
Input capacitors should be placed close to the IC and
connected to ground plane.
The GND and Exposed Pad should be connected to a
strong ground plane for heat sinking and noise protection.
The connection of R
noisy traces. The short wire is recommended to prevent
noise coupling.
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Figure 9. Derating Curves for RT9511 Packages
= (125 C
0
JA
JA
. For RT9511 packages, the Figure 9 of
is 52 C/W on the standard JEDEC 51-7
A
25
= 25 C can be calculated by following
Ambient Temperature (°C)
25 C) / (52 C/W) = 1.923W for
SETA
50
should be isolated from other
WQFN-24L 4x4
75
J(MAX)
Four Layers PCB
RT9511
www.richtek.com
and thermal
100
125
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