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Date: 7/19/04

SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator

© Copyright 2004 Sipex Corporation

APPLICATIONS INFORMATION

SP6648LEDEB Evaluation Board with

LumiLED High Brightness White LED

For the high brightness LumiLED white LED

application, the SP6648 is generally programmed

to set the operating current of the white LED as

equation:

current of the LumiLED. To set the operating

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

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 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

the forward voltage of the LumiLED. When the

LumiLED is open, the Feedback pin voltage

will go to 0V and the output voltage will go to

3.3V which will protect the part.

SP6648LEDEB Evaluation Board Schematic

SP6648LEDEB Efficiency Curve

60

65

70

75

80

85

90

95

100

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

Battery Voltage (V)

SP6648

V

BATT

1

LBI

2

R

LIM

4

SHDN

5

FB

6

GND

7

P

GND

8

LBON

3

LX

9

V

OUT

10

16.2k

D2

1W LED

D1 1N4148

Rb

1.8Ω

C1

10µF

C2

10µF

1.8-3.2V

10K

Important:

needed for stable regulation

350mA

C4

1µF

L1 10µH

1.87K