Datasheet

ADM8843
Rev. C | Page 13 of 16
APPLICATIONS
LAYOUT CONSIDERATIONS AND NOISE
Because of the ADM8843’s switching behavior, 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 ADM8843.
WHITE LED SHORTING
If an LED is shorted, the ADM8843 continues to drive the
remaining LEDs with I
LED
per LED (I
LED
= I
SET
× 120 mA). This
is because the ADM8843 uses four internal current sinks to
produce the LED current. If an LED is shorted, the ADM8843
continues to sink (I
SET
× 120 mA).
DRIVING FOUR LEDS IN THE MAIN DISPLAY ONLY
The ADM8843 can be operated with four LEDs in the main
display only (see Figure 23). With this configuration, CTRL1
and CTRL2 are used together to control the main display
shutdown operation and brightness control.
DRIVING FEWER THAN FOUR LEDS
The ADM8843 can be operated with fewer than four LEDs in
parallel by simply leaving the unused FBx pins floating or by
connecting them to GND. For example, Figure 24 shows three
LEDs being powered by the ADM8843.
V
OUT
FB1
FB2
FB3
FB4
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8843
05050-024
LCD
R
SET
I
SET
Figure 23. Driving Four White LEDs
V
OUT
FB1
FB2
FB3
FB4
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8843
05050-025
MAIN DISPLAY
R
SET
I
SET
Figure 24. Driving Three White LEDs
V
OUT
FB1
FB2
FB3
FB4
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8843
R
SET
I
SET
05050-002
MAIN DISPLAY
SUB DISPLAY
Figure 25. Typical Application Diagram