CD74HC4051: Unused input pin of CD74HC4051

Skylar Li

Intellectual 1990 points

Part Number: CD74HC4051

Tool/software:

Hi Experts,

This is Skylar responsible for GREE.

GREE wants to know that if they have unused input pin of CD74HC4051, what do you recommend for it, floating it, pullup or pulldown? Thanks.

BR,

Skylar

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 317250 points

When you have high-frequency (RF) signals, unused I/O pins should be connected to GND with a 50 Ω resistor. But in most cases, signals are slower, so it does not matter and you can let them float.

All control input pins must have a valid logic voltage.

0 Skylar Li over 1 year ago in reply to Clemens Ladisch

TI__Intellectual 1990 points

Hi Clemens,

Could you pls clarify the sentence: All control input pins must have a valid logic voltage? Thanks.

BR,

Skylar

0 Clemens Ladisch over 1 year ago in reply to Skylar Li

Guru 317250 points

S0/S1/S2/E are digital control inputs. They must never be left floating.

The A pins are analog I/Os and can be left floating.

+1 Kalin Burnside over 1 year ago

TI__Genius 13300 points

Hello Skylar,

I'm assuming by "input pin" you mean one of the 8 source pins of the switch. It's fine to leave one or a few of these floating as long as the application isn't using high frequency signals. If you did mean one of the control pins (i.e. Sx, or E) then Clemens is correct in that you should not leave them floating and always have a known state for those pins.

Please check out the following FAQ for more information on unused pins:

[FAQ] What to do with Unused Pins & Exposed Thermal Pads?

Regards,

Kalin Burnside

Switches & multiplexers

Switches & multiplexers forum

CD74HC4051: Unused input pin of CD74HC4051

[FAQ] What to do with Unused Pins & Exposed Thermal Pads?