LP3944 Datasheet, PDF (10/12 Pages) National Semiconductor (TI) – RGB/White/Blue 8-LED Fun Light Driver

Application Notes (Continued)
Address 0x05 (PWM1)
Bit #
7
6
5
4
3
2
1
0
Default value
1
0
0
0
0
0
0
0
PWM1 register determines the duty cycle of DIM1. The LED outputs are LOW (LED on) when the count is less than the value in PWM1 and HIGH (LED off) when
it is greater. If PWM1 is programmed with 0x00, LED output is always HIGH (LED off).
The duty cycle of DIM1 is: PWM1/256
Default value is 50% duty cycle.
BINARY FORMAT FOR SELECTOR REGISTERS — ADDRESS 0x06 to 0x07
Bit #
Default value
7
6
0
0
B1
B0
LED3
Address 0x06 (LS0)
5
4
0
0
B1
B0
LED2
3
2
0
0
B1
B0
LED1
1
0
0
0
B1
B0
LED0
Bit #
Default value
7
6
0
0
B1
B0
LED7
Address 0x07 (LS1)
5
4
0
0
B1
B0
LED6
3
2
0
0
B1
B0
LED5
1
0
0
0
B1
B0
LED4
LED States With Respect To Values in "B1" and "B0"
B1
B0
0
0
0
1
1
0
1
1
Programming Example:
Dim LEDs 0 to 7 at 1 Hz at 25% duty cycle
Function
Output Hi-Z
(LED off)
Output LOW
(LED on)
Output dims
(DIM0 rate)
Output dims
(DIM1 rate)
Step 1: Set PSC0 to achieve DIM0 of 1s
Step 2: Set PWM0 duty cycle to 25%
Step 3: Set PSC1 to achieve DIM1 of 0.2s
Step 4: Set LEDs 0 to 7 to point to DIM0
Step
1
2
3
4
Description
Set DIM0 = 1s
1 = (PSC0 + 1)/160
PSC0 = 159
Set duty cycle to 25%
Duty Cycle = PWM0/256
PWM0 = 64
Set DIM1 = 0.2s
0.2 = (PSC1 + 1)/160
PSC1 = 31
LEDs 0 to 7
Output = DIM0
Register Name
PSC0
PWM0
PSC1
LS0, LS1
Set to (Hex)
0x09F
0x40
0x1F
LS0 = 0xAA
LS1 = 0xAA
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