Datasheet

Preliminary Technical Data EVAL–ADM8845
9 REV. PrB 02/05
Insert the following links to evaluate the ADM8845 part with both the main and sub display on, brightness controlled by a DC voltage
applied to the V
BRIGHT
node , SMB J8.
1. Insert LK1 – LK6, this attaches all 6 LEDS to the Vout pin (Pin 3) of the ADM8845 chip. We are now going to operate the ADM8845
Eval Board with 6 LEDs in parallel.
2. Insert LK7 A and LK8 A. This turns on both the main and sub display.
3. Insert LK10 A and LK 9 A. This connects in the 13.4K Ohm resistor to ground and also the 15K Ohm resistor.
4. Apply a DC voltage from 0V to 2.5V to adjust the current flowing through the 6 LEDs, thereby adjusting their brightness.
5. The Following formula describes the relationship between I
SET
and I
LED
I
SET
= (1/R
SET
+ 1/R)(V
SET
) – (1/R)(V
BRIGHT
)
I
LED
= 120 * I
SET
Where R = 15K Ohm, V
SET
= 1.18V (Voltage at I
SET
pin)
6. Remove all other Links
7. Apply power to Power Connector J1 (3V Nominal). This power up the ADM8845
ADM8845/6
I
SET
V
BRIGHT
R = 15K
R
SET
= 13.4K
0V - 2.5V
Figure 8. V
BRIGHT
Node
V
BRIGHT
I
LED
2.5V
1.6V
0.8V
0V
0mA
7.2mA
13.6mA
20mA
Figure 9. V
BRIGHT
Node Operation