AN2841

Description of LED dimming

7/31

Figure 2.

PWM serial-parallel conversion for multiple LED applications

Figure 3.

Example of a specific lighting setting

The following equation is used to determine how many LEDs can used in an application with

specific maximum SPI speed and PWM resolution requirements:

Equation 1

where;

N is the maximum number of LEDs

n is the PWM resolution

SERIAL DATA

Output 1- (LED1)

Output 2-(LED2)

Output 3-(LED3)

Output 4-(LED4)

1111

t

t

t

t

t

4% duty cycle

14% duty cycle

3% duty cycle

99% duty cycle

LEVELS

T PWM

1101 0101 0001

0000 1111 or new

data

T SEND_DATA

PARALLELDATA

AM00343

PWM

n

SPI

f

f

N

2

=