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SC4215A Datasheet(PDF) 6 Page - Semtech Corporation

Part No. SC4215A
Description  Very Low Input /Very Low Dropout 2 Amp Regulator With Enable
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Maker  SEMTECH [Semtech Corporation]
Homepage  http://www.semtech.com
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SC4215A Datasheet(HTML) 6 Page - Semtech Corporation

   
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 2005 Semtech Corp.
www.semtech.com
SC4215A
POWER MANAGEMENT
Introduction
The SC4215A 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
SC4215A 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 SC4215A is extremely tolerant of
output 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.
Internal voltage selection: By connecting the FB pin to
GND, an internal resistor divider will regulate the output
voltage to 1.0V.
If the FB pin is connected directly to the VO pin, the out-
put voltage will be regulated to the 0.5v internal refer-
ence.
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
Enable: Pulling this pin below 0.4V turns the regulator
off, reducing the quiescent current to a fraction of its
operating value. A pull up resistor up to 400kOhms should
be connected from this pin to the VIN pin in application
where supply voltages of 1.4V<Vin<1.9V is required. For
applications with higher voltages than 1.9V, EN pin could
be left open or connected to VIN.
Thermal Considerations
The power dissipation in the SC4215A is approximately
equal to the product of the output current and the input to
output 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 us-
ing 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.


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