SP6683 Datasheet, PDF(10/14 Page) Sipex Corporation – High Power LED Driver for Parallel Configuration

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SP6683 Datasheet, PDF (10/14 Pages) Sipex Corporation – High Power LED Driver for Parallel Configuration

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Component Selection

The guideline for selecting divider resistors is as

follows. For high input voltage, the SP6683 will

work in X1 mode. When the input voltage drops

to VTH threshold voltage, it will switch to X1.5

mode automatically. The VTH threshold voltage

for mode change can be calculated by:

VTH = (VF + 0.315 + m â¢ ILED â¢ ROUT)

Where VF and m are the forward voltage and

number of the white LEDs, Rout is the output

resistance of the SP6683.

The equation for the voltage divider R1 and R2

with VMODE = 1.25V is:

VTH = 1.25V â¢ (1+R1/R2)

Which can be expressed as R1:

R1 = [(VTH/1.25) - 1] R2

For the typical SP6683 application, using VF =

3.6V, m = 8, ILED = 15mA, ROUT = 6â¦, VTH will

be 4.63V, Select R2 = 100kâ¦, then R1 = 270kâ¦

APPLICATION INFORMATION

Ceramic capacitors are recommended for their

inherently low ESR, which will help produce

low peak-to-peak output ripple, and reduce high

frequency spikes.

The fly capacitor controls the strength of the

charge pump. Selection of the fly capacitor is a

tradeoff between the output voltage ripple and

the output current capability. Decreasing the fly

capacitor will reduce the output voltage ripple

because less charge will be delivered to the

output capacitor. However, a smaller fly capaci-

tor leads to larger output resistance, thus de-

creasing the output current capability and the

efficiency of the circuit. Increasing the value of

the input and output capacitors could further

reduce the input and output ripple. For back-

lighting applications up to 80mA output current,

CIN = COUT = 1ÂµF is typically used. For appli-

cations with more than 80mA output current, for

example in Flash applications where Iout can be

as much as 200mA, CIN = COUT = 2.2ÂµF is

recommended. For peak performance, place all

capacitors as close to the SP6683 as possible.

Refer to table 1 below for some suggested low

ESR capacitors.

Manufacturers/ Website

TDK/www.tdk.com

Murata/www.murata.com

SUGGESTED LOW ESR CAPACITORS

Part Number

C1005X5R0J105M

C1608X5R0J225K

GRM155R60J105KE19B

GRM188R61A225KE34B

Capacitance/

Voltage

1uF/6.3V

2.2uF/6.3V

1uF/6.3V

2.2uF/6.3V

Capacitor

Size/Type/Thickness

0402/X5R/0.5mm

0603/X5R/0.9mm

0402/X5R/0.55mm

0603/X5R/0.9mm

ESR at

100KHz

0.03

0.02

0.03

0.02

Date: 3/31/06 RevG

SP6683 1X/1.5X Charge Pump LED Driver for Flash or Backlight

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