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CD74HC4067: Pull down resistors on input?

David Daminelli
Prodigy 80 points
Part Number: CD74HC4067
Other Parts Discussed in Thread: MUX508

Hi!

Lately i've been working redesigning an old project. Here's a schematic from the old design:

PR1 and PR2 are resistor arrays; the output goes to a buffer amp op, and the inputs "SIGN*" came from a Hall Current Sensor. The buffer output will be read by a ADC converter.

As I've said, i'm redesigning this circuit, the first change that i made is using the CD74HC4067 instead DG406. Now, i'm thinking about this resistors arrays, and that's my question: Do i need them? SGN1-SGN16 are analog signals, and i cant see an advantage in use them (but i cant see a disadvantage too). I've search on internet but i couldnt find a really definitive answer. Can someone help, please?

 

  • 0
    TI__Mastermind 45625 points
    David,

    The ADG406 device can support a wide voltage supply range and in the circuit you have above it is +/- 12 V. The CD74HC4067 doesn't support that wide voltage range only single supply up to 6 V. To support +/- 12 V you will need a device like the MUX508.

    The multiplexers are passive FET switches and do not need any external components to operate. I believe your resistor array is a pull down resistor? If the hall sensor doesn't require a pull down resistor on the output the signal switch doesn't require a pull down.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Prodigy 80 points

    Thanks Adam!

    The Hall sensor's output is a 0-5V signal, so we dont need a +-12V supply, the 5V supply is enough (at least, thats what i think, and as i tested i didnt had any issues with the 5V single supply).