7400 Series Guide: 74HC18/74LS18 (4-input NAND gates)

The 74×18 (ex 74LS18) is a chip that comes packed with two 4-input Schmitt trigger NAND gates.

Learn how it works and how to use it with this beginner-friendly guide and start using NAND gates in your projects.

74HC18 / 74LS18 Package And Pinout

What does the 74HC18 / 74LS18 do?

The 74×18 gives you two 4-input NAND gate Schmitt trigger that you can use individually. A NAND gate is a logic gate that outputs 0 (LOW) only if all of its inputs are 1 (HIGH). In the truth table below, you can see what the output will be for any given input:

NAND gate truth table
Truth table for the NAND gate

How To Use This Chip

The 74LS18 comes in a 14-pin package, and you need to connect it to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One difference between the HC and LS version of the chip is that the 74HC18 supports 2V to 6V, while the 74LS18 only supports 5V.

The maximum current you can pull out of one output pin is 4 mA when the pin is high (sourcing) or 16 mA when the pin is low (sinking). This can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, you can use any of the two 4-input NAND gate Schmitt trigger inside.

7400 series IC connected to 5V on a breadboard
The 74HC18/74LS18 IC connected to power

74×18 Pinout

The 74×18 has 14 pins and contains two 4-input NAND gate Schmitt trigger laid out as shown in the pinout diagram below:

74LS18 Pinout
Pin #TypeDescription
1InputInput to the first NAND gate.
2InputInput to the first NAND gate.
3NCNot in use (Not Connected).
4InputInput to the first NAND gate.
5InputInput to the first NAND gate.
6OutputOutput from the first NAND gate.
7PowerConnect to ground (GND).
8OutputOutput from the second NAND gate.
9InputInput to the second NAND gate.
10InputInput to the second NAND gate.
11NCNot in use (Not Connected).
12InputInput to the second NAND gate.
13InputInput to the second NAND gate.
14PowerPositive power supply (VCC). Connect to +5V power.
Pin overview for the 74×18 IC

Alternatives and Equivalents for 74HC18 / 74LS18

There are many versions of the 74×18 chip. They all have the same functionality, but with different specifications such as supported voltages and maximum current output.

Here’s a list of a few equivalents of this chip:

  • 74HC18 (High-speed CMOS)
  • 74HCT18 (High-speed CMOS, TTL compatible)
  • 74LS18 (High-speed TTL)
  • 74LVC18 (Low Voltage TTL)
  • 74AC18 (Advanced CMOS)
  • 74ALS18 (Advanced Low-Power Schottky TTL)
  • 74F18 (Very High Speed)
  • 74C18 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC18 and SN74LS18 by Texas Instruments.

Can’t find the 74×18 anywhere? Then try one of the following IC alternatives:

  • 74×13 – Dual 4-input NAND gate (with Schmitt-trigger inputs).
  • 74×20 – Dual 4-input NAND gate
  • 74×22 – Dual 4-input NAND gate
  • 74×40 – Dual 4-input NAND gate (with buffered outputs).

If you can’t find the 74×18 IC in your local electronics store, don’t worry, you’ll most likely find it in one of the stores listed on this page of online stores where you’ll find components and tools for all your electronics projects.

Datasheet for the 74LS18 and 74HC18 chips

Download the PDF datasheet for your version of the 74×18 here:

Leave a Comment