PCA9551_8

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 08 — 31 July 2008

4 of 26

NXP Semiconductors

PCA9551

[1]

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

16

14

supply voltage

Table 2.

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