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CD4051 8-Channel Analog Mux

One analog pin becomes eight. Bidirectional, so it multiplexes sensors into an ADC or fans a signal back out.

Cheat sheet (SVG)

Logic level: 3-18 V (CD4051), 2-10 V (74HC4051)
Package: PDIP-16 / SOIC-16

1.Pinout diagram

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Pins 1-8

CD4051

Pins 9-16

Pin detail

Hover a pin for its mappings and gotchas. Click to keep it here.

Logic level: 3-18 V (CD4051), 2-10 V (74HC4051)
Package: PDIP-16 / SOIC-16

Fig. 1. CD4051 8-Channel Analog Mux, PDIP-16. Hover or tap a signal to light up every pin that carries it.

2.Watch out

It is a set of analog switches, not a buffer, so it works in both directions. The same chip reads eight sensors into one ADC pin or routes one DAC out to eight places.
On-resistance is around 125 ohm for the CD4051 and under 100 for the 74HC4051, and it varies with the signal level. Feeding a high-impedance load is fine; feeding anything that draws current puts a voltage across that resistance and the reading is wrong.
An ADC with a sample-and-hold needs time to charge through that resistance. Settle for a few microseconds after switching channels before sampling, or every reading carries a smear of the previous channel.
Three address pins select the channel, A is the low bit. INH high disconnects everything, which is how you parallel several chips onto one bus.
VEE is the negative analog rail. Tie it to ground for single-supply work; tie it to a negative rail and the chip will pass signals that swing below ground, which no microcontroller input can do alone.
The channel pins are scattered around the package in no sensible order. Wire from the numbers.
For 16 channels the CD4067 is the same idea with four address pins.

3.Minimum circuit

What has to go around the chip before it will run.

Fig. 2. Minimum circuit, drawn from Table 1. Crossing wires are not connected.

Table 1. External parts, and why each one is there.
Part	Between	Why
Wire link	VEE (7) to GND	VEE sets the bottom of the analog range. On a single supply it goes to ground, and it must go somewhere.
Wire link	INH (6) to GND	Inhibit is active high. Held high, all eight channels stay disconnected.
100 nF	VDD (16) to GND	Supply decoupling at the pin.

VDD sets the largest signal the switches will pass, and the three address pins are digital inputs that must be driven, never left floating. With VEE on a negative rail the part switches signals that swing below ground, which is the reason to choose a 4051 over a 74HC4051.

4.Full pin reference

Every pin, alias and mapping. This is the table that prints.

Table 2. Pin assignments.

Complete pin reference for CD4051 8-Channel Analog Mux
Pin	Name	Also called	Functions	Notes
1	CH4ADC	-	Channel 4
2	CH6ADC	-	Channel 6
3	COMADC	Z, COMMON	Common in/out	The single pin that connects to whichever channel is selected.
4	CH7ADC	-	Channel 7
5	CH5ADC	-	Channel 5
6	INH	E, ENABLE	Inhibit, active high	Ground it to enable. High disconnects all eight channels.
7	VEEVSS to -VDD	-	Negative analog supply	Tie to ground for single supply. A negative rail here lets signals swing below ground.
8	VSS	GND	Ground
9	C	S3, A2	Address bit 2
10	B	S2, A1	Address bit 1
11	A	S1, A0	Address bit 0	Low bit of the channel number.
12	CH3ADC	-	Channel 3
13	CH0ADC	-	Channel 0
14	CH1ADC	-	Channel 1
15	CH2ADC	-	Channel 2
16	VDD3-18 V	-	Positive supply	Sets the maximum signal the switches will pass. 100 nF at the pin.

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CD4051B, 4 alternatives

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