ESD Active High

Discussion in 'General Electronics Chat' started by blazin, Feb 4, 2014.

  1. blazin

    Thread Starter New Member

    Jun 4, 2012
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    I'm stuck with an IC that has an Active High power down input. We are currently seeing some behavior that I believe is attributed to lack of a pulldown and EM events raising the input above the switching region. Any suggestions on an ESD solution for an active high reset line? I'm thinking something like the following:

    [​IMG]
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    It would help if you gave us all relevant circuit details. Like which IC and some sort of schematic
     
  3. blazin

    Thread Starter New Member

    Jun 4, 2012
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    IC datasheet is not available to general public.

    3.3V power down input, if it is high, device clock is halted and counters are reset. No other information available on the data sheet, ie timing but I can envision this line breaking the threshold and intermittently disabling the device.

    Currently, input is driven by NC7WZ14 approximately 4 ft away, nothing else holding the line low.

    Sorry I don't have more info to provide..
     
  4. Brevor

    Active Member

    Apr 9, 2011
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    How fast does need to respond to a power down event, could you use a RC filter on the input.
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What is the input impedance of the power-down pin? Are we talking CMOS or ....?
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    A pull-down resistor?

    Why don't you have a pull down resistor on a 4 foot long wire to a critical function IC input? :eek:

    Capacitors can be useful things too.
     
    ErnieM likes this.
  7. blazin

    Thread Starter New Member

    Jun 4, 2012
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    Not sure, garbage data sheet does not give a requirement for the time this pin needs to be high.


    Again does not say, All i've got is data for 1.8V logic, 1.26V min VIH, 0.54 max VIL, 10 pf CIN.

    Agreed, that's my first order of business, tacking a pulldown near the chip, there is some internal pulldown referenced, but I'm sure it's something like 100k.

    I was handed this circuit and am trying to fix it. Thanks for your help!
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a resistor of fairly high value, not enough current to effect the circuit, is a good idea on input lines, a little load will keep static from building up and load down spikes.
     
  9. blazin

    Thread Starter New Member

    Jun 4, 2012
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    So just the pull down?
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If the fucntion of the pin is slow (like a stable ON/OFF mode) it is a great idea to add a cap there too, from the pin to ground, close to the chip.

    0.1uF is ok. Larger can be better especially if you have been getting issues of noise spikes on that line.
     
  11. blazin

    Thread Starter New Member

    Jun 4, 2012
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    Just measured the line back at the driver, 15ns rise up to ~2.9V, doesn't cause immediate disable but eventually, maybe 5-10 pulses, and it disables the stream.

    I'll drop a 3.74k in parallel with a 1uF, this is a critical piece of our system
     
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