SP6682 Datasheet, PDF (7/13 Pages) Sipex Corporation – High Efficiency Charge Pump Regulator for White LEDs

SP6682
High Efficiency White LED Charge Pump Regulator
different applications, as shown in figures 12-
14.
Figure 12 shows a circuit using the SP6682 to
drive discrete white LEDs as a current source.
Fig. 12: Driving Discrete White LEDs as Current Source
The current in one white LED current is set by
the ratio of the feedback pin voltage (306mV)
and the bias resistor RB. To set the operating
current, RB can be selected by:
R_B
=
V_FB
I _LED
The current of the remaining white LEDs is set
according to the similarity of the white LEDs.
A 3-wire white LED module with internal series
resistors as shown in figure 13 can also be
driven in this way.
Fig. 14: Driving 2-Wire White LED Module
as Current Source
In this application, the bias resistor can be
selected by:
R_B
=
V_FB
I _LED(TOTAL)
Where I_LED(TOTAL) is the total operating current
of all the white LEDs.
To use the SP6682 as a voltage source for
fixed voltage applications, a voltage divider is
needed to program the ouput voltage, as
shown in Figure 15.
Fig. 15: Driving 2-Wire White LED Module
as Voltage Source
Fig. 13: 3-Wire White LED Module
In Figure 14, the SP6682 was used to drive a
2-wire white LED module without internal
series resistors as a current source. The bias
resistor RB is selected to regulate the total
current of the white LED module in-stead of
the current of single LED as in Figure 12.
The output voltage is set by the ratio of the
two resistors and the feedback control voltage
as shown by:
V_OUT
= _{⎜⎜⎝⎛}1+
R₅
R₆
⎟⎟⎠⎞
×V_FB
PROGRAMMING THE OPERATING MODE
SP6682 can automatically change from X1.5
mode to X2 mode for highest efficiency. To
© 2009 Exar Corporation
7/13
Rev. 2.0.0