SP6683EU Sipex, SP6683EU Datasheet - Page 4

• Manufacturer Part Number: SP6683EU
• Description: High Power LED Driver for Parallel Configuration
• Manufacturer: Sipex

Date: 07/07/04
General Overview
The SP6683 is a current regulated charge pump
ideal for converting a Li-Ion battery input for
driving white LEDs used in backlighting color
displays in cellular phones, PDAs, digital cam-
eras and MP3 players. The SP6683 is able to
efficiently drive up to eight 20mA white LEDs
in parallel and maintain a constant brightness
over a very wide operating voltage range (2.7V
to 5.5V). The SP6683 operates with an internal
1.2MHz clock, enabling the use of small exter-
nal components. Other features of SP6683 in-
clude PWM dimming control as well as com-
plete input/out disconnect in shutdown. In shut
down mode the IC draws less than 1.5µA cur-
rent. The output regulation is achieved by sens-
ing the voltage at the feedback pin and modulat-
ing the switch between the charge pump and
output capacitor.
Theory of Operation
The SP6683 regulated charge pump block dia-
gram consists of four main blocks (Voltage
Reference, Mode Control, Clock Manager, Start-
up and Charge-Pump Switches) and two com-
parators (V
parator).
1) Voltage Reference. This block provides the
306mV and 1.25V reference voltages needed
for the two comparators.
2) Mode Control. An external voltage divider
connected to the V
voltage to the mode comparator which sets the
logic state of the mode selection outputs to the
X1 or X1.5 modes. V
1.25V bandgap voltage. For example, if one
makes a 158K/100K divider, the mode will
change at 2.58 x 1.25 V =3.23V. A comparator-
based cycle by cycle regulation ensures that no
mode change occurs during cycles.
3) Clock Manager. An internal 1.2MHz clock
is generated in this block. Depending on the
mode control, the appropriate clock phasing is
generated here and sent to the start-up and
charge-pump switches block.
MODE
Comparator and V
MODE
MODE
pin will define an input
is compared to a
SP6683 White LEDs Driver for Parallel Configuration
OUT
Com-
4
Figure 9. Driving discrete white LEDs as current source
4) V
306mV reference voltage is compared to feed-
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:
where V
Configuring the SP6683 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 SP6683 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 SP6683 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
current, R
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
OUT
SP6683
8
FB
Comparator and Output Control. A
R
GND
B
B
= 306mV.
can be selected by:
= V
V
OUT
I
FB
LED
FB
I
OUT
1
5
1uF
© Copyright 2004 Sipex Corporation
= V
B
. To set the operating
R
FB
FB
Rb
OPERATION
Rb