LP3944

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SNVS264A – MAY 2004 – REVISED APRIL 2013

Table 6. Address 0x05 (PWM1)(1)

Bit #

7

6

5

4

3

2

1

0

Default value

1

0

0

0

0

0

0

0

(1)

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 0x07Table 7

Table 7. Address 0x06 (LS0)

Bit #

7

6

5

4

3

2

1

0

Default value

0

0

0

0

0

0

0

0

B1

B0

B1

B0

B1

B0

B1

B0

LED3

LED2

LED1

LED0

Table 8. Address 0x07 (LS1)

Bit #

7

6

5

4

3

2

1

0

Default value

0

0

0

0

0

0

0

0

B1

B0

B1

B0

B1

B0

B1

B0

LED7

LED6

LED5

LED4

Table 9. LED States With Respect To Values in "B1" and "B0"

B1

B0

Function

0

0

Output Hi-Z

(LED off)

0

1

Output LOW

(LED on)

1

0

Output dims

(DIM0 rate)

1

1

Output dims

(DIM1 rate)

Programming Example:

Dim LEDs 0 to 7 at 1 Hz at 25% duty cycle

1. Set PSC0 to achieve DIM0 of 1s

2. Set PWM0 duty cycle to 25%

3. Set PSC1 to achieve DIM1 of 0.2s

4. Set LEDs 0 to 7 to point to DIM0

Step

Description

Register Name

Set to (Hex)

1

Set DIM0 = 1s

PSC0

0x09F

1 = (PSC0 + 1)/160

PSC0 = 159

2

Set duty cycle to 25%

PWM0

0x40

Duty Cycle = PWM0/256

PWM0 = 64

3

Set DIM1 = 0.2s

PSC1

0x1F

0.2 = (PSC1 + 1)/160

PSC1 = 31

4

LEDs 0 to 7

LS0, LS1

LS0 = 0xAA

Output = DIM0

LS1 = 0xAA

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