pca9551bs3 NXP Semiconductors, pca9551bs3 Datasheet - Page 6

• Manufacturer Part Number: pca9551bs3
• Description: 8-bit I2c Led Driver With Programmable Blink Rates
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA9551_7
Product data sheet
6.3.3 PWM0 - Pulse Width Modulation 0
6.3.4 PSC1 - Frequency Prescaler 1
6.3.5 PWM1 - Pulse Width Modulation 1
Table 5.
The PWM0 register determines the duty cycle of BLINK0. The outputs are LOW (LED off)
when the count is less than the value in PWM0 and HIGH when it is greater. If PWM0 is
programmed with 00h, then the PWM0 output is always LOW.
The duty cycle of BLINK0 = (256
Table 6.
PSC1 is used to program the period of the PWM output.
The period of BLINK1 = (PSC1 + 1) / 38.
Remark: Prescaler calculation is different between the PCA9551 and other PCA955x
LED blinkers. A divider ratio of 38 instead of 44 is used. This different divider ratio causes
the blinking frequency to be 13 % (1
The programmed value of Frequency Prescaler 1 must be adjusted to compensate for this
difference in applications where the PCA9551 is used in conjunction with other PCA955x
LED blinkers and the observed blinking frequencies need to be the same.
Table 7.
The PWM1 register determines the duty cycle of BLINK1. The outputs are LOW (LED off)
when the count is less than the value in PWM1 and HIGH when it is greater. If PWM1 is
programmed with 00h, then the PWM1 output is always LOW (LED off).
The duty cycle of BLINK1 = (256
Table 8.
Bit
Symbol
Default
Bit
Symbol
Default
Bit
Symbol
Default
Bit
Symbol
Default
PSC0 - Frequency Prescaler 0 register description
PSC0[7]
PWM0 - Pulse Width Modulation 0 register description
PSC1 - Frequency Prescaler 1 register description
PSC1[7]
PWM1 - Pulse Width Modulation 1 register description
PWM0
PWM1
[7]
[7]
7
1
7
1
7
1
7
1
PSC0[6]
PSC1[6]
Rev. 07 — 23 February 2007
PWM0
PWM1
[6]
[6]
6
1
6
0
6
1
6
0
8-bit I
PSC0[5]
PSC1[5]
PWM0
PWM1
[5]
[5]
5
1
5
0
5
1
5
0
PWM0) / 256.
PWM1) / 256.
2
C-bus LED driver with programmable blink rates
38 / 44) lower when the same 8-bit word is used.
PSC0[4]
PSC1[4]
PWM0
PWM1
[4]
[4]
4
1
4
0
4
1
4
0
PSC0[3]
PSC1[3]
PWM0
PWM1
[3]
[3]
3
1
3
0
3
1
3
0
PSC0[2]
PSC1[2]
PWM0
PWM1
[2]
[2]
2
2
0
2
2
0
1
1
PCA9551
PSC0[1]
PSC1[1]
© NXP B.V. 2007. All rights reserved.
PWM0
PWM1
[1]
[1]
1
1
1
0
1
1
1
0
PSC0[0]
PSC1[0]
PWM0
PWM1
[0]
[0]
0
1
0
0
0
1
0
0
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