SP6648 datasheet(12/16 Pages) SIPEX

12 / 16 page

Date: 6/7/06 Rev B

SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator

APPLICATIONS INFORMATION

SP6648LEDEB Evaluation Board with

LumiLED High Brightness White LED

For the high brightness LumiLED white LED

application, the SP6648 is generally programmed

as a current source. The bias resistor Rb is used

to set the operating current of the white LED in

the equation:

Rb = VREF/IF

where VREF is around 0.61V, IF is the operating

current of the LumiLED. To set the operating

current to be about 350mA, Rb is selected as 1.8 Ω

as shown in the following schematic. The effi-

ciency of the SP6648 LumiLED circuit is im-

proved by the use of a silicon diode D1 and

resistor R1 to set the voltage at the current sense

resistor R2 to 0.61V instead of the higher 1.25V

at the FB pin. An efficiency curve follows

showing the SP6648 efficiency driving 350mA

output current into the high brightness LumiLED.

As shown in following scope photos, if the

SP6648 is powered up before the LumiLED is

plugged in, the circuit will bring the Feedback

pin to 0.0V and the SP6648 has a feature to set

the output voltage to be 3.3V. Once the LumiLED

is plugged in, the Feedback pin will go up to

1.25V and begin to regulate. The output voltage

will go from 3.3V to 3.68V (=VF+0.61V), where

VF is the forward voltage of the LumiLED.

When the LumiLED is open, the Feedback pin

voltage will go to 0.0V and the output voltage

will go to 3.3V which will protect the part.

SP6648LEDEB Evaluation Board Schematic

SP6648LEDEB Efficiency Curve

100

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

Battery Voltage (V)

SP6648

BATT

LBI

LIM

SHDN

GND

LBON

OUT

16.2k

1W LED

D1 1N4148

1.8Ω

10µF

1.8-3.2V

(R5 optional)

10K

VREF = 0.61V

Important:

1µF Ceramic Cap at VOUT Pin

needed for stable regulation

350mA

IOUT=0.61V/Rb

1µF

L1 10µH

VBATT

RLIM

1.87K

SP6648 Datasheet(PDF) 12 Page - Sipex Corporation

SP6648 Datasheet(HTML) 12 Page - Sipex Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL