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PCA9551BS,118

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26
PCA9551_8 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 08 — 31 July 2008 4 of 26
NXP Semiconductors
PCA9551
8-bit I
2
C-bus LED driver with programmable blink rates
[1] HVQFN16 package die supply ground is connected to both V
SS
pin and exposed center pad. V
SS
pin must
be connected to supply ground for proper device operation. For enhanced thermal, electrical, and board
level performance, the exposed pad needs to be soldered to the board using a corresponding thermal pad
on the board and for proper heat conduction through the board, thermal vias need to be incorporated in the
PCB in the thermal pad region.
6. Functional description
Refer to Figure 1 “Block diagram of PCA9551”.
6.1 Device address
Following a START condition, the bus master must output the address of the slave it is
accessing. The address of the PCA9551 is shown in Figure 5. To conserve power, no
internal pull-up resistors are incorporated on the hardware selectable address pins and
they must be pulled HIGH or LOW.
The last bit of the address byte defines the operation to be performed. When set to logic 1
a read is selected, while a logic 0 selects a write operation.
6.2 Control register
Following the successful acknowledgement of the slave address, the bus master will send
a byte to the PCA9551, which will be stored in the Control register.
The lowest 3 bits are used as a pointer to determine which register will be accessed.
LED7 12 10 LED driver 7
RESET 13 11 reset input (active LOW)
SCL 14 12 serial clock line
SDA 15 13 serial data line
V
DD
16 14 supply voltage
Table 2. Pin description
…continued
Symbol Pin Description
SO16, TSSOP16 HVQFN16
Fig 5. PCA9551 slave address
002aac505
1 1 0 0 A2 A1 A0 R/W
fixed
slave address
hardware
selectable
Reset state: 00h
Fig 6. Control register
002aac506
0 0 0 AI 0 B2 B1 B0
register address
Auto-Increment flag
PCA9551_8 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 08 — 31 July 2008 5 of 26
NXP Semiconductors
PCA9551
8-bit I
2
C-bus LED driver with programmable blink rates
If the Auto-Increment (AI) flag is set, the three low order bits of the Control register are
automatically incremented after a read or write. This allows the user to program the
registers sequentially. The contents of these bits will rollover to ‘000’ after the last register
is accessed.
When the Auto-Increment flag is set (AI = 1) and a read sequence is initiated, the
sequence must start by reading a register different from ‘0' (B2 B1 B0 ≠ 000).
Only the 3 least significant bits are affected by the AI flag. Unused bits must be
programmed with zeroes.
6.2.1 Control register definition
6.3 Register descriptions
6.3.1 INPUT - Input register
The INPUT register reflects the state of the device pins. Writes to this register will be
acknowledged but will have no effect.
Remark: The default value ‘X’ is determined by the externally applied logic level (normally
logic 1) when used for directly driving LED with pull-up to V
DD
.
6.3.2 PSC0 - Frequency Prescaler 0
PSC0 is used to program the period of the PWM output.
The period of BLINK0 = (PSC0 + 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 − 38 / 44) lower when the same 8-bit word is used.
The programmed value of Frequency Prescaler 0 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 3. Register summary
B2 B1 B0 Symbol Access Description
0 0 0 INPUT read only input register
0 0 1 PSC0 read/write frequency prescaler 0
0 1 0 PWM0 read/write PWM register 0
0 1 1 PSC1 read/write frequency prescaler 1
1 0 0 PWM1 read/write PWM register 1
1 0 1 LS0 read/write LED0 to LED3 selector
1 1 0 LS1 read/write LED4 to LED7 selector
Table 4. INPUT - Input register description
Bit 7 6 5 4 3 2 1 0
Symbol LED7 LED6 LED5 LED4 LED3 LED2 LED1 LED0
Default XXXXXXXX
PCA9551_8 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 08 — 31 July 2008 6 of 26
NXP Semiconductors
PCA9551
8-bit I
2
C-bus LED driver with programmable blink rates
6.3.3 PWM0 - Pulse Width Modulation 0
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 − PWM0) / 256.
6.3.4 PSC1 - Frequency Prescaler 1
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 − 38 / 44) lower when the same 8-bit word is used.
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.
6.3.5 PWM1 - Pulse Width Modulation 1
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 − PWM1) / 256.
Table 5. PSC0 - Frequency Prescaler 0 register description
Bit 7 6 5 4 3 2 1 0
Symbol PSC0[7] PSC0[6] PSC0[5] PSC0[4] PSC0[3] PSC0[2] PSC0[1] PSC0[0]
Default 11111111
Table 6. PWM0 - Pulse Width Modulation 0 register description
Bit 7 6 5 4 3 2 1 0
Symbol PWM0
[7]
PWM0
[6]
PWM0
[5]
PWM0
[4]
PWM0
[3]
PWM0
[2]
PWM0
[1]
PWM0
[0]
Default 10000000
Table 7. PSC1 - Frequency Prescaler 1 register description
Bit 7 6 5 4 3 2 1 0
Symbol PSC1[7] PSC1[6] PSC1[5] PSC1[4] PSC1[3] PSC1[2] PSC1[1] PSC1[0]
Default 11111111
Table 8. PWM1 - Pulse Width Modulation 1 register description
Bit 7 6 5 4 3 2 1 0
Symbol PWM1
[7]
PWM1
[6]
PWM1
[5]
PWM1
[4]
PWM1
[3]
PWM1
[2]
PWM1
[1]
PWM1
[0]
Default 10000000
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PCA9551BS,118

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Buy PCA9551BS,118
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NXP Semiconductors
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LED Lighting Drivers 8-BIT I2C FM OD LED
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