SC620 Datasheet, PDF (14/16 Pages) Semtech Corporation – Octal LED Driver, General Purpose Current Sink with Serial Interface

POWER MANAGEMENT
Application Examples (Cont.)
Backlighting with Series Connected LEDs connected to a Boosted Output Voltage
SC620
5V
1μF
DC/DC Boost Voltage
Boost
limiting
R₂ = (3/7)*(R₁)
+
-
R₁
Limit SC620 sink pins to < [VIN – 1.5]
2
SC620
5
VIN
ILED1
11
SCL
SCL
6
ILED2
10
SDA
SDA
7
ILED3
3
EN
EN
8
ILED4
1
GND
13
ILED5
4
GND
14
ILED6
9
GND
15
ILED7
12
GND
16
ILED8
LED Backlighting
Example Circuit
This application example uses the SC620 to drive 32
LEDs in a 4-in-series by 8-in-parallel arrangement. Other
arrangements of series and parallel combinations are
possible.
The operating voltage limit of [VIN - 1.5V] at the sink pins
must be observed to achieve the specified accuracy of the
device.
To prevent the boost voltage from illuminating the LEDs
while the current sinks are off, the boost voltage must
follow the SC620 in the start-up sequence. The boost
voltage must also power-off before the current sinks turn
off in the shut-down sequence. Protection diodes are
necessary to protect the current sinks from destructive
voltage levels produced by the boost voltage supply.
© 2006 Semtech Corp.
14
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