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74HC595 VS 74LS595, 74HC595 VS 74HC164, 74HC595 vs MCP23017

  • Contents

Executive Summary: 2026 Component Comparison

The Verdict: For modern embedded systems in 2026, the 74HC595 remains the superior choice for general-purpose output expansion due to its integrated latching capability and CMOS efficiency.

  • Vs. 74LS595: The LS series is effectively obsolete; use HC for lower power and wider voltage tolerance.
  • Vs. 74HC164: Choose the 595 to prevent LED flickering (ghosting) during data shifting.
  • Vs. MCP23017: Use the MCP23017 only when you need bidirectional I/O or I2C communication; otherwise, the 74HC595 is faster and cheaper.

The 74HC595 remains one of the most ubiquitous shift registers in electronics engineering as of 2026. While it is a staple component, selecting the right alternative requires understanding the nuances of latching, protocols, and power consumption.

 

In this updated engineering guide, we analyze the 74HC595 against its primary alternatives: the legacy 74LS595, the non-latched 74HC164, and the I2C-based MCP23017. We will determine interchangeable use cases and performance benchmarks for modern applications.


What is the difference between 74HC595 and 74LS595?

Direct Answer: The fundamental difference is the underlying technology; the 74HC595 uses modern High-speed CMOS (low power, flexible voltage), while the 74LS595 uses obsolete TTL (high power, fixed 5V).

Comparison diagram of 74HC595 CMOS vs 74LS595 TTL shift registers

Component Datasheets (PDF)

74HC595 Datasheet (Updated)
74LS595 Datasheet (Legacy)

74HC595 Technical Overview

The 74HC595 is a high-speed CMOS 8-bit shift register with a storage register (latch) and 3-state outputs. It is fabricated with silicon gate C2MOS technology, allowing it to operate efficiently across a voltage range of 2V to 6V.

 

Key Features:

  • Architecture: 8-bit serial-in, parallel-out shift register feeding an 8-bit D-type storage register.
  • Clocking: Separate clocks for the shift register and storage register (positive-edge triggered).
  • Cascading: Includes a serial output (Q7S) for chaining multiple chips without signal degradation.

74LS595 Technical Overview (Legacy)

The 74LS595 is the older Low-power Schottky (LS) predecessor. While functionally similar regarding pinout logic, it is strictly bound to TTL logic levels (5V).

 

It features the same 8-bit serial-in/parallel-out architecture with separate clocks. However, its bipolar transistor construction results in significantly higher quiescent current consumption compared to the HC series.

Critical Comparison: HC vs. LS Series

  • Technology Standard: 74HC595 is CMOS based (Current Standard). It offers high noise immunity and low power consumption. The 74LS595 is TTL based (Obsolete BJT technology).

  • Power Efficiency: CMOS technology (HC) draws near-zero static current, whereas TTL (LS) requires constant base current for its bipolar transistors, making LS unsuitable for battery-powered devices in 2026.

  • Voltage Flexibility: The 74HC series operates typically between 2V and 6V, making it compatible with 3.3V microcontrollers (like ESP32/STM32). The 74LS series requires a strict 5V ±5% supply.

  • Input Impedance: HC devices have high input impedance (requiring less drive current from the microcontroller), while LS devices have lower impedance, loading down the bus.


Why choose 74HC595 over 74HC164? (Latching Explained)

Direct Answer: The 74HC595 is superior for driving LEDs because it contains an output latch, whereas the 74HC164 outputs data immediately as it shifts, causing visible flickering or "ghosting."

Pinout comparison 74HC595 vs 74HC164 shift register

Component Datasheets

74HC595 Datasheet
74HC164 Datasheet

74HC164 Operational Basics

The 74HC164 is a simpler 8-bit serial-in/parallel-out shift register. It lacks the storage register found in the 595.

 

Data enters serially through DSA or DSB. Crucially, the outputs (Q0-Q7) change state immediately on every LOW-to-HIGH transition of the clock (CP). There is no "holding" buffer.

Key Differences: Buffer and Control

The 74HC595 is generally preferred in modern circuit design for the following reasons:

  • The Latch Factor (Visual Stability): The 74HC595 buffers data. You shift 8 bits in invisibly, then toggle the latch pin to update all outputs simultaneously. The 74HC164 shows every shift step on the output pins. If driving LEDs, the '164' creates a strobing effect as bits ripple through.

  • Cascading Method: The 74HC595 uses a dedicated serial output pin (Q7') for cascading, leaving the parallel outputs unaffected. The 74HC164 requires sacrificing the last parallel output (Q7) to drive the next chip.

  • Output Enable (OE): The 74HC595 features an Output Enable pin, allowing the microcontroller to turn off all outputs (High-Z) via software (useful for PWM brightness control). The 74HC164 lacks this feature.

  • Reset Logic: 74HC595 reset clears the shift register but not the latch (unless re-latched). The 74HC164 Master Reset (MR) clears outputs immediately and asynchronously.


Shift Register vs. IO Expander: 74HC595 or MCP23017?

Direct Answer: Use the 74HC595 for high-speed, output-only tasks (like LED walls); use the MCP23017 when you need bidirectional pins (Input/Output) and prefer the I2C protocol to save microcontroller pins.

74HC595 DIP package vs MCP23017 I/O Expander

Component Datasheets

74HC595 Datasheet
MCP23017 Datasheet

MCP23017 Operational Basics

The MCP23017 is a sophisticated 16-bit I/O Expander. Unlike a shift register, it functions as a peripheral device that communicates via the I2C bus. It provides 16 fully configurable GPIO pins that can act as inputs (with internal pull-ups) or outputs.

Detailed Analysis: Speed vs. Flexibility

1. Directionality
The 74HC595 is Output Only (Serial to Parallel). The MCP23017 is Bidirectional (can read buttons or sensors).

 

2. Interface Speed
Shift registers (SPI-like) are extremely fast. You can pump data into a 74HC595 at 20MHz+ (hardware SPI). The MCP23017 uses I2C, which typically runs at 400kHz or 1.7MHz. For high-refresh-rate LED displays, the 74HC595 is the winner.

 

3. Pin Count efficiency
A 74HC595 requires 3 pins (Data, Clock, Latch). The MCP23017 requires 2 pins (SDA, SCL) and can share that bus with 100+ other sensors. If your microcontroller is pin-constrained, I2C is often better.

 

Summary Recommendation:

  • Driving LEDs/Relays? Use 74HC595. It is cheaper, faster, and easier to code.
  • Reading Keypads/Sensors? Use MCP23017. It handles inputs and interrupts natively.

74HC595D,118 Documents & Media

Download datasheets and manufacturer documentation for Nexperia USA Inc. 74HC595D,118.

74HC595D,118 PCB Symbol, Footprint & 3D Model

Nexperia USA Inc. 74HC595D,118

Nexperia USA Inc.

IC SHIFT REGISTER 8BIT 16SOIC

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Daisy

Daisy is a seasoned technical writer with over 9 years of experience in the semiconductor industry. She possesses a deep understanding of the field and can explain complex technical concepts in a clear and concise manner. Daisy is skilled at crafting various types of technical documentation, including white papers, case studies, product briefs, and technical articles.

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