PCA9557: 2.3-5.5V I2C/I2C/SMBus 8-Bit Low-Power IO Expander with Configurable Inputs & Latched Outputs

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PCA9557是一款由TI公司设计的8位I/O扩展器，专为2.3V至5.5V电压范围的I2C总线（两线双向总线）操作而优化。该设备通过I2C接口（包括串行时钟SCL和串行数据SDA）为各种微控制器家族提供通用的远程I/O扩展功能。这款扩展器的核心特性包括： 1. 低功耗设计：PCA9557在待机模式下具有极低的电流消耗，最大仅为1μA，这对于电池供电应用非常有利。 2. 内置电源复位：设备在上电时自动执行内部复位，确保系统稳定启动。 3. 高阻抗开漏输出：P0引脚支持高阻抗开漏输出，允许它直接驱动LED，提供强大的驱动能力。 4. I2C与并行接口转换：它将I2C信号转换为并行接口，便于与多种外设连接。 5. 初始配置：所有通道在上电时默认配置为输入，可通过写入I/O配置位来改变其功能。 6. 宽电源范围：支持2.3V至5.5V的工作电压，确保了广泛的设备兼容性。 7. 无上电抖动：当电源接通时，不会有数据信号的瞬间失真，提高了信号的稳定性。 8. 5V耐受输入：输入端口能够承受5V电压，增加了其电气兼容性。 9. 噪声滤波：内置SCL和SDA输入噪声滤波器，有助于提高数据传输的准确性。 10. 高速I2C支持：支持400kHz的快速I2C通信速率，适合对速度有要求的应用。 11. 高电流驱动的锁定输出：输出端口具有高电流驱动能力，可以直接驱动大量LED，非常适合显示控制。 12. 地址选择灵活性：三个硬件地址引脚允许最多连接8个设备到I2C或SMBus总线上，支持多设备组网。 PCA9557是一款功能强大、功耗低的I2C扩展器，适用于需要灵活、低功耗I/O扩展的嵌入式系统，特别适合于需要通过I2C通信连接外部设备的场合，如LED照明控制、传感器接口等。

Device Address

Slave Address

0 1 1 A2 A1 A0

R/W

Fixed Programmable

Control Register and Command Byte

0 0 0 0 B1 B000

PCA9557

www.ti.com

.................................................................................................................................................... SCPS133I – DECEMBER 2005 – REVISED JUNE 2008

The address of the PCA9557 is shown in Figure 4 .

Figure 4. PCA9557 Address

Address Reference

INPUTS

C BUS SLAVE ADDRESS

A2 A1 A0

L L L 24 (decimal), 18 (hexadecimal)

L L H 25 (decimal), 19 (hexadecimal)

L H L 26 (decimal), 1A (hexadecimal)

L H H 27 (decimal), 1B (hexadecimal)

H L L 28 (decimal), 1C (hexadecimal)

H L H 29 (decimal), 1D (hexadecimal)

H H L 30 (decimal), 1E (hexadecimal)

H H H 31 (decimal), 1F (hexadecimal)

The last bit of the slave address defines the operation (read or write) to be performed. A high (1) selects a read

operation, while a low (0) selects a write operation.

Following the successful acknowledgment of the address byte, the bus master sends a command byte that is

stored in the control register in the PCA9557. Two bits of this data byte state the operation (read or write) and

the internal registers (input, output, polarity inversion or configuration) that will be affected. This register can be

written or read through the I

C bus. The command byte is sent only during a write transmission.

Once a new command byte has been sent, the register that was addressed continues to be accessed by reads

until a new command byte has been sent.

Figure 5. Control Register Bits

Command Byte

CONTROL REGISTER BITS

COMMAND BYTE POWER-UP

(HEX) DEFAULT

B1 B0

0 0 0x00 Input Port Read byte xxxx xxxx

0 1 0x01 Output Port Read/write byte 0000 0000

1 0 0x02 Polarity Inversion Read/write byte 1111 0000

1 1 0x03 Configuration Read/write byte 1111 1111

Product Folder Link(s): PCA9557

Power-On Reset

RESET

PCA9557

SCPS133I – DECEMBER 2005 – REVISED JUNE 2008 ....................................................................................................................................................

www.ti.com

The input port register (register 0) reflects the incoming logic levels of the pins, regardless of whether the pin is

defined as an input or an output by the configuration register. It only acts on read operation. Writes to these

registers have no effect. The default value, X, is determined by the externally applied logic level.

Before a read operation, a write transmission is sent with the command byte to signal the I

C device that the

input port register will be accessed next.

BIT I7 I6 I5 I4 I3 I2 I1 I0

DEFAULT X X X X X X X X

The output port register (register 1) shows the outgoing logic levels of the pins defined as outputs by the

configuration register. Bit values in this register have no effect on pins defined as inputs. In turn, reads from this

BIT O7 O6 O5 O4 O3 O2 O1 O0

DEFAULT 0 0 0 0 0 0 0 0

The polarity inversion register (register 2) allows polarity inversion of pins defined as inputs by the configuration

register. If a bit in this register is set (written with 1), the corresponding port pin ' s polarity is inverted. If a bit in this

BIT N7 N6 N5 N4 N3 N2 N1 N0

DEFAULT 1 1 1 1 0 0 0 0

The configuration register (register 3) configures the directions of the I/O pins. If a bit in this register is set to 1,

the corresponding port pin is enabled as an input with high impedance output driver. If a bit in this register is

cleared to 0, the corresponding port pin is enabled as an output.

BIT C7 C6 C5 C4 C3 C2 C1 C0

DEFAULT 1 1 1 1 1 1 1 1

When power (from 0 V) is applied to V

, an internal power-on reset holds the PCA9557 in a reset condition until

has reached V

POR

. At that time, the reset condition is released, and the PCA9557 registers and I

C/SMBus

state machine initialize to their default states. After that, V

must be lowered to below 0.2 V and back up to the

operating voltage for a power-reset cycle. The RESET input can be asserted to reset the system, while keeping

the V

at its operating level.

A reset can be accomplished by holding the RESET pin low for a minimum of t

. The PCA9557 registers and

C/SMBus state machine are held in their default states until RESET again is high. This input requires a pullup

resistor to V

if no active connection is used.

Product Folder Link(s): PCA9557

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