SP6648UEB Exar Corporation, SP6648UEB Datasheet - Page 12

• Manufacturer Part Number: SP6648UEB
• Description: Power Management Modules & Development Tools Ultra Low Quies Cur Hi-Eff Boost Reg
• Manufacturer: Exar Corporation
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of SP6648UEB

• Product: Power Management Modules

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 R
to set the operating current of the white LED in
the equation:
R
SP6648LEDEB Evaluation Board Schematic
SP6648LEDEB Efficiency Curve
Date: 6/7/06 Rev B
b
V
= V
BATT
100
REF
95
90
85
80
75
70
65
60
1.8
/I
1.8-3.2V
F
C1
10µF
2.0
R
1.87K
LIM
2.2
Battery Voltage (V)
2.4
1
2
3
4
5
2.6
V
LBI
LBON
R
SHDN
BATT
LIM
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator
2.8
L1 10µH
SP6648
3.0
b
GND
P
V
is used
3.2
GND
FB
OUT
LX
10
9
8
7
6
12
Important:
1µF Ceramic Cap at V
needed for stable regulation
C4
1µF
where V
current of the LumiLED. To set the operating
current to be about 350mA, R
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 R
resistor R
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 (=V
V
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.
F
is the forward voltage of the LumiLED.
REF
R
16.2k
1
2
1
APPLICATIONS INFORMATION
R
I
OUT
to set the voltage at the current sense
to 0.61V instead of the higher 1.25V
5
is around 0.61V, I
10K
(R
=0.61V/R
OUT
5
optional)
Pin
D1 1N4148
b
C2
10µF
b
is selected as 1.8 Ω
© 2006 Sipex Corporation
F
F
+0.61V), where
is the operating
V
Rb
1.8Ω
REF
D2
1W LED
350mA
= 0.61V