Datasheet

ADM8845
Rev. C | Page 14 of 20
APPLICATIONS
LAYOUT CONSIDERATIONS AND NOISE
Because of the s switching behavior of the ADM8845, PCB trace
layout is an important consideration. To ensure optimum
performance, a ground plane should be used, and all capacitors
(C1, C2, C3, C4) must be located with minimal track lengths to
the pins of the ADM8845.
WHITE LED SHORTING
If an LED is shorted, the ADM8845 continues to drive the
remaining LEDs with I
LED
per LED (I
LED
= I
SET
× 120 mA). This
is because the ADM8845 uses six internal currents sinks to
produce the LED current. If an LED is shorted, the ADM8845
continues to sink (I
SET
× 120 mA) as programmed by R
SET
through the shorted LED.
DRIVING FEWER THAN SIX LEDs
The ADM8845 can be operated with fewer than six LEDs in
parallel by simply leaving the unused FBx pins floating or
connected to GND. For example, Figure 28 shows five LEDs
being powered by the ADM8845, and Figure 29 shows three
main LEDs and one sub LED.
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
04867-0-029
LCD
Figure 28. Driving Five White LEDs
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
R
SET
I
SET
04867-0-030
MAIN DISPLAY
SUB DISPLAY
Figure 29. Driving Three Main LEDs and One Sub LED
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
R
SET
I
SET
04867-0-002
MAIN DISPLAY
SUB DISPLAY
Figure 30. Typical Application Diagram