Application Examples (Cont.)

Backlighting with Series Connected LEDs connected to a Boosted Output Voltage

SC620

VIN

2

SCL

11

SDA

10

EN

3

GND

1

GND

4

GND

9

GND

12

ILED1

5

ILED2

6

ILED3

7

ILED4

8

ILED6

14

ILED7

15

ILED8

16

ILED5

13

1μF

SCL

SDA

EN

LED Backlighting

5V

Limit SC620 sink pins to < [VIN – 1.5]

+

-

DC/DC Boost Voltage

Boost

limiting

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.

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.

The operating voltage limit of [VIN - 1.5V] at the sink pins

must be observed to achieve the specified accuracy of the

device.

14

© 2006 Semtech Corp.

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POWER MANAGEMENT

SC620