SP6682 Datasheet, PDF (6/12 Pages) Sipex Corporation – High Efficiency Charge Pump Regulator for White LEDs

encing high input voltages. Another important
operation of this block is the PWM/EN dim-
ming control, which is implemented in the delay
of each pump driver, so that the enable high
pulse width is proportional to the delay of the
individual pump switches.
5) V_OUT Comparator and Output Control. A
306mV reference voltage is compared to feed-
Configuring the SP6682 as Voltage or
Current Source
The white LED load configuration used by
customers can be discrete white LEDs or a white
LED module. Inside the white LED module,
there may or may not be resistors in series with
the white LEDs. According to the different
application requirements, the SP6682 can be
configured as either a voltage source or a current
source to provide solutions for these different
applications, as shown in figure 9~12. Figure 9
shows using the SP6682 to drive discrete white
LEDs as a current source.
The current in one white LED current is set by
the ratio of the feedback pin voltage (306mV)
and the bias resistor R_B. To set the operating
current, R_B can be selected by:
R_B = ^VFB
I_LED
V_OUT
1
SP6682
5
FB
Rb
Rb
GND
2.2uF
8
OPERATION: Continued
back output voltage to control the Vout needed
for the application. Output current is set by a
bias resistor from FB pin to GND pin chosen by
the relationship:
I_OUT = ^VFB
R_FB
where V_FB = 306mV.
APPLICATION INFORMATION
The current of the remaining white LEDs is set
according to the similarity of the white LEDs. 3-
wire white LED module with internal series
resistors as shown in figure 10 can also be driven
in this way.
Anode
FB
3-wire W-LED module
GND
Fig 10. 3-wire white LED module
In figure 11, SP6682 was used to drive a 2-wire
white LED module without internal series resis-
tors as a current source. The bias resistor R_B is
selected to regulate the total current of the white
LED module instead of the current of single
LED as in figure 9.
V_{OUT 1}
Anode
SP6682
5
V_FB
GND
8
2-wire W-LED module
Cathode
Rb
Figure 9. Driving discrete white LEDs as current source
Figure 11. Driving 2-wire white LED module as current
source
Date: 5/5/04
SP6682 High Efficiency Charge Pump Regulator for White LEDs
© Copyright 2004 Sipex Corporation
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