Overview
The PCF8579HT is a CMOS integrated circuit that provides 8-bit general purpose parallel input/output (I/O) expansion for most microcontroller families via the two-line bidirectional bus (I2C). It's particularly useful when the microcontroller runs out of I/O pins or when additional I/O is needed while minimizing wiring complexity. As a member of the PCF857x family of I/O expanders, this device offers simple I2C interface compatibility, requiring only two microcontroller pins for control. The PCF8579HT is commonly used in industrial control systems, automation equipment, and various embedded applications where additional I/O is required.
Structure and Working Principle
The PCF8579HT consists of an 8-bit quasi-bidirectional I/O port, I2C-bus interface logic, and three hardware address pins that allow up to eight devices to share the same I2C-bus. The quasi-bidirectional I/O port eliminates the need for direction control registers, simplifying software implementation. When the I2C interface receives data from the microcontroller, it latches the data to the output port. Conversely, reading operations return the current state of the input pins. The device operates with power supply voltages ranging from 2.5V to 6V, making it compatible with both 3.3V and 5V systems.
Key Features
The PCF8579HT offers several notable features including low standby current consumption (typically 10μA), high output drive capability for directly driving LEDs, and compatibility with most microcontroller families. The device supports clock frequencies up to 400kHz in Fast-mode I2C operation. Additional features include latched outputs with high-current drive capability for directly driving LEDs, interrupt output that can be connected to the interrupt logic of the microcontroller, and three hardware address pins allowing connection of up to eight devices to the same I2C-bus. These features make it particularly useful in space-constrained applications.
Application Areas
The PCF8579HT finds applications in various fields including industrial control panels, where it's used to expand I/O for sensor monitoring and actuator control. It's commonly employed in automotive electronics for dashboard controls and in consumer electronics for button matrix scanning. Other applications include home automation systems, where it can control relays and read switch inputs, and in test equipment where additional I/O is needed for instrumentation control. The device's ability to directly drive LEDs makes it popular in display applications without requiring additional driver circuits.
Maintenance and Precautions
When working with the PCF8579HT, proper ESD precautions should be observed during handling and installation. The device should be stored in anti-static packaging when not in use. During operation, ensure that the power supply voltage does not exceed the maximum rating of 6V to prevent damage. For reliable operation, proper decoupling capacitors (typically 0.1μF) should be placed close to the power pins. When designing PCB layouts, keep I2C trace lengths short and consider adding pull-up resistors appropriate for the chosen bus speed. The interrupt line should be properly terminated if used.
B2B Procurement Guide
When procuring PCF8579HT ICs in bulk, consider purchasing from authorized distributors to ensure authenticity and quality consistency. Verify the packaging type (TSSOP, SO, etc.) matches your production requirements. Lead times may vary depending on market conditions. For prototype or small quantity orders, many electronics component distributors offer samples. For high-volume applications, negotiate pricing based on projected annual usage. Consider alternative part numbers in the PCF857x family if specific features aren't required, as these may offer cost savings.