Datasheet

EVAL-ADM8843 Preliminary Technical Data
10 REV. PrC 02/05
Insert the following links to evaluate the ADM8843 part with both the main and sub display on, brightness controlled by a PWM signal
applied to the V
PWM
node , SMB J4.
1. Insert LK2 – LK5, this attaches all 4 LEDS to the Vout pin (Pin 3) of the ADM8843 chip. We are now going to operate the ADM8843
Eval Board with 4 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 B. This connects in the 13.4K Ohm resistor to ground and also the two 7.5K Ohm resistors and the 1µF
capacitor to ground between them.
4. Apply a PWM signal (Amplitude from 0V - 2.5V only) to adjust the current flowing through the 6 LEDs, thereby adjusting their
brightness.
5. The Following formula describes the relationship between V
PWM
and I
LED
I
LED
= I
SET_Voltage * 120 * (1 - Duty Cycle)
RSET * 2R 100
RSET + 2R
Where R = 7.5K 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 ADM8843.
100% = I
LED
=0mA
0% = I
LED
= 20mA
ADM8843
I
SET
V
PWM
C5 = 1µF
R=7.5K
R = 7.5K
R
SET
=13.4K
0V - 2.5V
Figure 10. V
PWM
Node Operation