CD74HC4067 S0-S3 current draw and using the MUX in series with others and parallel with others.

James Claypool

Other Parts Discussed in Thread: CD74HC4067

1. What is the input current necessary to drive the S0-S3 and enable input pins of the CD74HC4067 1:16 MUX/DEMUX?

2. Can the CD74HC4067 be placed in series with a second and when doing so, what is the power drop across the 2 MUX's as a result?

3. If I were to use the MUX in a backplane configuration, can you place the input pins in parallel so that multiple MUX's are able to be supplied with the same S0-S3 and enable values, but they are only driven on when 5V is supplied to that part of the system? Essentially 10 MUX's have the same S0-S3, enable and ground pins and the 5V is sourced for each part of the system when you want to turn it on. the 5V that is being supplied is also being driven by another CD74HC4067.

over 9 years ago

0 ShreyasRao over 9 years ago

TI__Guru 62170 points

Hi James ,

The CMOS inputs of S0-S3 and enable have high input impedance due to which the input current requirement is small. The input leakage will be 1uA on the input and hence this can be tied to be fanned out all in parallel.

0 James Claypool over 9 years ago in reply to ShreyasRao

Prodigy 30 points

Thank you, do you know if there is a current drop when tying two MUX's together in series? For example I have the first MUX output as the COM input to the second MUX then the first output of that MUX is feeding a relay.

0 ShreyasRao over 9 years ago in reply to James Claypool

TI__Guru 62170 points

The switches are bilateral switches which ideally should have no voltage drop between them. Most switches do not have distortions from I/O except for small drop depending on the Ron of the switch . I do not foresee problems connecting the COM of 1st device into COM of the 2nd device . Care must be taken to avoid contentions on either side .

0 James Claypool over 9 years ago in reply to ShreyasRao

Prodigy 30 points

Thank you again. one final question, Is it necessary to include a small capacitor between COM and VCC and include a resistor from the input of enable to ground?

0 Emrys Maier over 9 years ago in reply to James Claypool

TI__Guru* 97046 points

Hi James,

Neither of those items is a necessity. A capacitor from Vcc to COM will attenuate high frequency signals, and a resistor from enable to ground will ensure that the device remains enabled even if that line is left floating.

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CD74HC4067 S0-S3 current draw and using the MUX in series with others and parallel with others.