SC5010 datasheet(25/36 Pages) SEMTECH

25 / 36 page

SC5010

Components Selection (continued)

160mA, and 1x 10μF or 2x 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/undershoots during load transient

and loop stability. Recommended ceramic capacitor

manufacturers are listed in Table 4.

Table 4 — Recommended Ceramic Capacitor Vendors

Vendor

Web site

Kemet

www.kemet.com

Vishay

www.vishay.com

TDK

www.tdk.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

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 4.7μF or larger ceramic

capacitor.

Output Freewheeling Diode Selection

Schottky diodes are the ideal choice for SC5010 due to

their low forward voltage drop and fast switching speed.

Table 5 shows several different Schottky diodes that work

properly with the SC5010. 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 5 — Recommended Rectifier Diodes

Rectifier Diode

Vendor Web site

DFLS140

www.diodes.com

1N5819HW

www.diodes.com

SS13/14/15/16, SS23/24/25/26

www.vishay.com

External Power MOSFET Selection

The boost converter in SC5010 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 SC5010 is not exposed to high

voltage. Only the external power MOSFET, freewheeling

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 R

(on) MOSFETs

are preferred for achieving better efficiency.

The GD (gate driver) on SC5010 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 following equation.

GATE = QG x fSW

G — Gate charge

The R

DS(ON)

and its RMS current I

S_RMS

of the power MOSFET

will generate the conduction loss using the following

equation.

COND = IS_RMS

x R

DS(on)

The MOSFET’s switch loss can be calculated using the fol-

lowing equation.

SW = ½ x VIN x IL_PEAK x fSW x (TON + TOFF)

Where T

ON and TOFF are the MOSFET’s on and off time

and they can be estimated by the following

equations.

Where t

, t

, Q

and V

plateau

can usually be found from data-

sheet of the selected MOSFET. R

is the resistance of the

optional resistor connected in series on the gate of the

MOSFET.

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