SC5014A View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC5014A
Semtech Corporation
'SC5014A' PDF : 27 Pages View PDF
SC5014A
Application Information (continued)
VRIPPLE – Peak to peak output ripple.
The ripple voltage should be less than 200mV (pk-pk) to
ensure good LED current sink regulation. For example, a
typical application where 240mA/string current is needed,
the total output current for 2 channels will be 480mA, and
6x 4.7µF capacitors are recommended.
During load transient, the output capacitor supplies or
absorbs additional current before the inductor current
reaches its steady state value. Larger capacitance helps
with the overshoot/undershoot during load transient and
loop stability.
Input Capacitor Selection
X5R or X7R ceramic capacitor is recommended for input
bypass capacitor. A 1µF capacitor is sufficient for the VCC
input. Bypass the VIN input with a 10µF or larger ceramic
capacitor.
Output Freewheeling Diode Selection
Schottky diodes are the ideal choice for the SC5014A due
to their low forward voltage drop and fast switching
speed. Table 3 shows several different Schottky diodes
that work properly with the SC5014A. Verify that the diode
has a voltage rating greater than the maximum possible
output voltage. The diode conducts current only when
the power switch is turned off. The diode must be rated to
handle the average output current. A diode rated for 1A
average current will be sufficient for most designs.
Table 3. Recommended Rectifier Diodes
Rectifier Diode
DFLS140
SS14/15/16, SS24/25/26
Vendor Website
www.diodes.com
www.vishay.com
diode and the inductor will be exposed to the output
voltage. The external power MOSFET should be selected
with its voltage rating higher than the output voltage by
minimum 30%. The current rating should be enough to
handle the inductor peak current. Low RDS(on) MOSFETs
are preferred for achieving better efficiency.
The GD (gate driver) on SC5014A provides 1A (peak)
current driving capability which is suitable for most
MOSFETs for high frequency operation. The average
current required to drive the MOSFET is given by the fol-
lowing equation.
IGATE = QG x fSW
QG — Gate charge
The RDS(ON) and its RMS current IS_RMS of the power MOSFET
will generate the conduction loss using the following
equation.
PCOND
=
I2
S_RMS
x
RDS(on)
The MOSFET’s switch loss can be calculated using the fol-
lowing equation.
PSW = ½ x VIN x IL_PEAK x fSW x (TON + TOFF)
Where TON and TOFF are the MOSFET’s on and off time
and they can be estimated by the following
equations.
( ) ( ) TON = tr +
Q gd
5 − Vplateau / 5 + Rg
( ) TOFF
=
tf
+
Qgd
Vplateau / 5 + Rg
External Power MOSFET Selection
The boost converter in SC5014A uses an external power
MOSFET to regulate the output voltage and output power
to drive LED loads. This boost switching structure has an
advantage in that the SC5014A is not exposed to high
voltage. Only the external power MOSFET, freewheeling
Where tr, tf, Qgd and Vplateau can usually be found from data-
sheet of the selected MOSFET. Rg is the resistance of the
optional resistor connected in series on the gate of the
MOSFET.
18
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