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SC4211 Datasheet(PDF) 6 Page - Semtech Corporation

Part No. SC4211
Description  Very Low Input /Very Low Dropout 1 Amp Regulator With Enable
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Maker  SEMTECH [Semtech Corporation]
Homepage  http://www.semtech.com
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SC4211 Datasheet(HTML) 6 Page - Semtech Corporation

   
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 2004 Semtech Corp.
www.semtech.com
SC4211
POWER MANAGEMENT
Thermal Considerations
The power dissipation in the SC4211 is approximately equal
to the product of the output current and the input to out-
put voltage differential:
()
O
D
I
VOUT
VIN
P
The absolute worst-case dissipation is given by:
()
Q(MAX)
(MAX)
O(MAX)
(MIN)
(MAX)
D(MAX)
I
VIN
I
VOUT
VIN
P
+
=
For a typical scenario, V
IN = 3.3V ± 5%, VOUT = 2.8V and
I
O = 1A, therefore:
V
IN(MAX) = 3.465V, VOUT(MIN) = 2.744V and IQ(MAX) = 1.75mA,
Thus P
D(MAX) = .722W.
Using this figure, and assuming T
A(MAX) = 70°C, we can cal-
culate the maximum thermal impedance allowable to main-
tain T
J ≤ 150°C:
() ()
C/W
110
.722
70
150
P
T
T
R
D(MAX)
A(MAX)
J(MAX)
A)(MAX)
TH(J
°
=
=
=
This should be achievable for the SOIC-8EDP package
using PCB copper area to aid in conducting the heat away,
such as one square inch of copper connected to the ground
pins of the device. Internal ground/power planes and air
flow will also assist in removing heat. For higher ambient
temperatures it may be necessary to use additional cop-
per area.
Introduction
The SC4211 is intended for applications where high cur-
rent capability and very low dropout voltage are required.
It provides a very simple, low cost solution that uses very
little PCB real estate. Additional features include an en-
able pin to allow for a very low power consumption standby
mode, and a fully adjustable output.
Component Selection
Input capacitor: A large bulk capacitance of about 100uF
should be closely placed to the input supply pin of the
SC4211 to ensure that Vin does not sag below 1.4V. Also a
minimum
of
4.7µF
ceramic
capacitor
is
recommended to be placed directly next to the Vin pin.
This
allows
for
the
device
being
some
distance from any bulk capacitance on the rail.
Additionally, input droop due to load transients is reduced,
improving load transient response. Additional capacitance
may be added if required by the application.
Output capacitor: a minimum bulk capacitance of 10µF,
along with a 0.1µF ceramic decoupling capacitor is
recommended. Increasing the bulk capacitance will
improve the overall transient response. The use of
multiple lower value ceramic capacitors in parallel to
achieve the desired bulk capacitance will not cause
stability issues. Although designed for use with ceramic
output capacitors, the SC4211 is extremely tolerant of out-
put capacitor ESR values and thus will also work
comfortably with tantalum output capacitors.
Noise immunity: in very electrically noisy environments, it
is recommended that 0.1µF ceramic capacitors be placed
from IN to GND and OUT to GND as close to the device pins
as possible.
External voltage selection resistors: the use of 1%
resistors, and designing for a current flow
≥ 10µA is
recommended to ensure a well regulated output (thus R2
≤ 120kΩ).
Applications Information


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