I am using these two ICs in my design: EEPROM CAV24Cxx and Analog MUX 74HC4851.

What is the value of input decoupling capacitor that I must connect near the Vcc pin?

The recommended value of the input decoupling capacitor on the Vcc pin is not mentioned in the datasheet or is it mentioned by someother name which I didn't see?

  • \$\begingroup\$ Use 0.1uF and 1Kohm in the various VDD lines to the analog MUX. Keep MCU trash away from the huge FETs inside the MUX, because the huge gates will be moving along with the VDD trash, and simply dumping the VDD trash onto the switch-channels. \$\endgroup\$ Commented Jan 29, 2019 at 5:16

1 Answer 1


Decoupling capacitors generally do not need to have a specific value.

Exceptions might be voltage regulators like LDOs which sometimes need a specific value (or a value that must be at least xx nF) for best stability. But your chips are logic chips, these aren't picky in that respect.

Most experienced engineers just use 100nF. If we would be using 82 nF somewhere in the circuit already, but not 100 nF, then we might use 82 nF to minimize the number of different components.

I would advise against using decoupling capacitors smaller than 47 nF and larger than 1 uF but that's just my guess.

Having too many decoupling caps is generally not an issue so if you have the space available feel free to add an extra (space for) a capacitor. It does not mean that a capacitor must be placed there. In commercial products you will see empty spaces on a PCB, an empty space is usually much cheaper than designing and manufacturing a new PCB!

If you're quite unsure and want to keep as many options open as possible and have enough PCB area then add footprints for placing extra and larger size capacitors. That way it will be easy to experiment with different values.

But in general: when not listed use 100 nF and chances are that that will do just fine.

  • \$\begingroup\$ Thank you. I couldn't find anywhere in the datasheet regarding this \$\endgroup\$
    – Freshman
    Commented Jan 23, 2019 at 8:33
  • 1
    \$\begingroup\$ You'll generally be fine at low speeds (<10 MHz), but when things get faster you need to think a bit more (as always). For e.g. edn.com/design/components-and-packaging/4351231/… \$\endgroup\$
    – awjlogan
    Commented Jan 23, 2019 at 10:04

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