Internal Pullup?

Discussion in 'General Electronics Chat' started by pntrbl, Sep 10, 2008.

  1. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    Due to the general confusion and chaos that seems to reign supreme in my life, I managed to order AH173 Hall-Effect sensors from Mouser when I had been using AH175's. The difference being the AH173 has an internal pullup resistor.

    I'm not understanding how that works tho. I thought a pull up was selected based on Vcc and the desired operating current. How can the 173 have the right pullup for the entire Vcc range?

    I'm gonna hook one up and see what happens when they get here, lol, but I'd like to know what I'm missing on this ....

    Thanx for any and all education on the subject.

    SP
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, the internal pull-up resistor is nominally 10k, but could be as low as 7k or as high as 13k. You could still use an external pull-up resistor if you felt that you wanted to source more current. However, if you're just going to be driving a CMOS or FET input, you probably won't need more current.

    Remember, that sensor can sink up to 25mA; but if you use an external pull-up resistor, you will have to take that into account.

    Right now, you're just supplying it with 12v and using the clipping diode for checking the output, right? The internal 10k resistor should be plenty.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I agree that you should be fine with the AH173 in place of the AH175 and an external pullup provided you observe the 25ma maximum drive current.

    The internal pullup version is probably available for those applications where space is at a premium.

    hgmjr
     
  4. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    0
    Thanx for the replies guys. Glad to hear it's pretty much a non-issue but it's good to know ...

    Still working at 12v and diode clipped Sarge. I did series up 3 diodes for 2v cuz it displays a lot better thru the noise I'm getting on WinScope. Haven't burned the soundcard yet ...:D

    SP
     
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