onsemi MC74HC595ADTG 8-Bit Shift Register IC: Datasheet, Pinout, and Application Circuit Guide

The MC74HC595ADTG from onsemi is a high-speed 8-bit serial-in, parallel-out shift register that has become a cornerstone in digital electronics design. This IC is renowned for its ability to expand the output capabilities of microcontrollers and other digital systems using a minimal number of GPIO pins. It is part of the high-speed CMOS (HC) family, offering the low power consumption of CMOS technology while maintaining the ability to drive relatively high currents.

This guide provides a detailed overview of its datasheet, pin configuration, and a fundamental application circuit.

Datasheet Overview and Key Specifications

The datasheet for the MC74HC595ADTG outlines its electrical characteristics and absolute maximum ratings. Key specifications include:

Supply Voltage Range (VCC): 2.0 V to 6.0 V. This allows for operation with various logic levels, including 3.3V and 5V systems.

High-Current Outputs: Each output (Q0-Q7) can sink or source up to 35 mA, making it capable of driving LEDs, relays, or other peripherals directly without additional drivers.

Low Power Consumption: Typical ICC of 80 μA, which is crucial for battery-powered applications.

Operating Temperature Range: -55°C to +125°C, suitable for industrial and automotive environments.

Package: The "DTG" suffix denotes a TSSOP-16 surface-mount package, which is compact for space-constrained PCB designs.

Pinout Configuration

Understanding the pinout is critical for circuit design. The MC74HC595ADTG has 16 pins:

1. Q0 to Q7 (Pins 1-7, 15): The 8 parallel output pins.

2. GND (Pin 8): Ground connection.

3. Q7' (Pin 9): Serial data output. This allows for daisy-chaining multiple shift registers to create longer chains (e.g., 16, 24 bits) from a single serial data source.

4. MR (Pin 10): Master Reset (active LOW). When pulled LOW, it asynchronously clears all bits in the shift register, setting outputs (Q0-Q7) to LOW.

5. SHCP (Pin 11): Shift Register Clock Input. On each LOW-to-HIGH transition, the value at the SER pin is shifted into the register.

6. STCP (Pin 12): Storage Register Clock Input (Latch Pin). On a LOW-to-HIGH transition, the data in the shift register is copied to the storage (output) register, updating the parallel outputs.

7. OE (Pin 13): Output Enable (active LOW). When LOW, the outputs are enabled. When HIGH, the outputs are in a high-impedance state, allowing them to be turned off without clearing the data.

8. DS (SER) (Pin 14): Serial Data Input.

9. VCC (Pin 16): Positive supply voltage.

Basic Application Circuit Guide

A typical application involves controlling multiple LEDs with a microcontroller (MCU) using only three GPIO pins.

Components Required:

MC74HC595ADTG IC

Microcontroller (e.g., Arduino, ESP32, PIC)

LEDs (x8) with current-limiting resistors (~220Ω)

Power supply (e.g., 5V)

A 0.1μF decoupling capacitor placed close to the VCC and GND pins

Circuit Connection:

1. Connect the MCU's three GPIO pins to the IC's DS (SER), SHCP, and STCP pins.

2. Connect the OE pin to GND to permanently enable the outputs (or control it with another MCU pin for blinking/blanking).

3. Connect the MR pin to VCC to disable the master reset function.

4. Connect each output pin (Q0-Q7) to the anode of an LED through a current-limiting resistor, with the LED cathodes connected to GND.

5. Provide power (5V) to VCC and connect GND to the common ground.

Operation Sequence:

To display a pattern (e.g., 0b10101010) on the LEDs:

1. The MCU sets the STCP (Latch) pin LOW.

2. The MCU clocks the SHCP (Shift Clock) pin and serially sends each bit of data to the DS (Data) pin, one bit per clock pulse (MSB or LSB first, as defined by your software).

3. After all 8 bits are shifted in, the MCU sets the STCP (Latch) pin HIGH. This latches the shifted data to the output register, instantly updating all eight parallel outputs (Q0-Q7).

ICGOODFIND: The onsemi MC74HC595ADTG is an exceptionally efficient and versatile solution for I/O expansion. Its ability to control multiple high-current outputs with minimal microcontroller pins, combined with features like daisy-chaining and output enable, makes it an indispensable component for a vast array of projects, from simple LED displays and relay banks to complex industrial control systems.

Keywords: Shift Register, I/O Expansion, Serial to Parallel, Daisy Chain, LED Driver.