7400 Series Guide: 74HC40/74LS40 (Dual 4-input NAND gates)

The 74×40 (ex 74LS40) is a cool little chip that has two 4-input NAND gates with buffered outputs.

In this guide, you will learn everything you need to know about this chip and how you can use 4-input NAND gates in your own projects.

What does the 74HC40 / 74LS40 do?

The 74×40 gives you two 4-input NAND gates with buffered output 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).

The fact that the output is buffered, just means that you can get more current out of it than a standard NAND gate.

How To Use This Chip

The 74LS40 comes in a 14-pin package, and you need to connect it to power before you can use it. It supports a VCC voltage of 5V (this might differ between models).

The maximum current you can pull out of one output of the 74ls40 pin is 1.2 mA when the pin is high (sourcing) or 24 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 gates with buffered output inside.

74×40 Pinout

The 74×40 has 14 pins and contains two 4-input NAND gates with buffered output laid out as shown in the pinout diagram below:

Pin #	Type	Description
1	Input	Input to the first NAND gate.
2	Input	Input to the first NAND gate.
3	NC	Not in use (Not Connected).
4	Input	Input to the first NAND gate.
5	Input	Input to the first NAND gate.
6	Output	Output from the first NAND gate.
7	Power	Connect to ground (GND).
8	Output	Output from the second NAND gate.
9	Input	Input to the second NAND gate.
10	Input	Input to the second NAND gate.
11	NC	Not in use (Not Connected).
12	Input	Input to the second NAND gate.
13	Input	Input to the second NAND gate.
14	Power	Positive power supply (VCC). Connect to +5V power.

Alternatives and Equivalents for 74HC40 / 74LS40

There are many versions of the 74×40 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:

• 74HC40 (High-speed CMOS)
• 74HCT40 (High-speed CMOS, TTL compatible)
• 74LS40 (High-speed TTL)
• 74LVC40 (Low Voltage TTL)
• 74AC40 (Advanced CMOS)
• 74ALS40 (Advanced Low-Power Schottky TTL)
• 74F40 (Very High Speed)
• 74C40 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74LS40 by Motorola.

Can’t find the 74×40 anywhere? Then try one of the following IC alternatives:

• 74×13 – Dual 4-input NAND gates (with Schmitt-trigger inputs).
• 74×18 – Dual 4-input NAND gates (with Schmitt-trigger inputs).
• 74×20 – Dual 4-input NAND gate buffers.
• 74×22 – Dual 4-input NAND gates (with open-collector outputs).
• CD4012 – Dual 4-input NAND gates.

If you can’t find the 74×40 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 74LS40 and 74HC40 chips

Download the PDF datasheet for your version of the 74×40 here:

• 74LS40 (Motorola)