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Mosfet Drivers and Input Hysteresis

Discussion in 'Electronic Design' started by D from BC, Jun 2, 2007.

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  1. D from BC

    D from BC Guest

    Isn't this a kickass mosfet driver?
    http://ixdev.ixys.com/DataSheet/99061.pdf
    IXYS ISDD414PI

    Anyways...as on the datasheet..
    Vih=3.5min
    Vil = 0.8Vmax..
    That just tells me the max hysteresis...
    The min hysteresis is unknown and the typical input hysteresis is
    unknown.
    Heck..I'm not even sure if chip has input hysteresis.. :p
    (I sent an email to IXYS Corp but it's the weekend...)

    I've noticed some Microchip drivers have 300mV input hysteresis..
    The max5048 has a whopping 1.6V of input hysteresis but no stock at
    Digikey..

    I want to put a slooooowwwww signal + some noise to a mosfet driver.
    Anybody know a mosfet driver that has something between 0.5V to 1V of
    input hysteresis?

    I suspect this is going to be a pita item to search for because input
    hysteresis is too "mickey mouse" to include on manufacturers selection
    tables..
    This means looking at every freakn datasheet...?
    Or should I just email a bunch of companies for the info?
    D from BC
     
  2. Joerg

    Joerg Guest


    It's customary to provide your own hysteresis ;-)

    Seriously, a couple of resistors do the trick. Or drive the driver with
    with Schmitt.
     
  3. D from BC

    D from BC Guest

    Yeah...but I'm trying to reduce the component count.. I make my own
    PCB's so if my circuits are low in components then I don't have to do
    much PCB drafting and fab..
    D from BC
     
  4. Or just spring for a Schmitt trigger input buffer (or build one).

    Robert
     
  5. D from BC

    D from BC Guest

    It might end up doing that if I have a favorite mosfet driver and I
    don't like it's input hysteresis :(
    I know many ways to create hysteretic circuits...I just don't want to
    include one.. :)
    D from BC
     
  6. Joerg

    Joerg Guest


    But then you'll be stuck with expensive boutique parts that hardly
    anybody else uses.
     
  7. legg

    legg Guest

    Make it work first. This is the wrong place to introduce a high
    impedance node.

    RL
     
  8. D from BC

    D from BC Guest

    The mosfet driver IC input will get a slow non square signal but it'll
    be from a relatively low impedance source.
    The input shouldn't flap around in the wind so to speak..
    But I'll check to see if anything else will kick the mosfet driver
    input.
    D from BC
     
  9. D from BC

    D from BC Guest

    Ahh.. but if the boutique parts speed up my project time..great!
    As long as the boutique parts stay at a insignificant cost level..
    Ex..I change $900.00 for a one off project.. One $4.00 boutique part
    is insignificant..
    D from BC
     
  10. legg

    legg Guest

    Turn the source into a comparator with hysterisis. This is the wrong
    place in the circuit to decide whether or not you want to switch. The
    decision should already have been made.

    Even under those conditions, you'll see drivers with hysterisis equal
    to 30% of the input logic supply rail - and for good reasons.

    RL
     
  11. Joerg

    Joerg Guest


    Ok then. As long as they don't have to build another one in three years
    and then your part has gone unobtanium.
     
  12. D from BC

    D from BC Guest

    Yeah..that's the risk...
    It could be good for business.. :p
    I just say
    "It's not my fault Supertex discontinued the part."
    I can make a new design with another part.. but that'll be another
    $900.00 :)
    Isn't that just evil :)

    I do recall on one design where I couldn't find a boutique part, did
    it the long way, did the pcb and then found a boutique part..
    Damn..
    So.I kept the original PCB artwork and merged in the artwork for the
    boutique part..
    So...if the boutique part got discontinued..the artwork exists for the
    fatter equivalent circuit.
    Then I turned the situation into a selling point.."Discontinued part
    resistant design". :)
    D from BC
     
  13. Joerg

    Joerg Guest

    Problem is, some day word gets around. Clients don't like that ;-)


    That's what my clients expect (and get) with every design...
     
  14. Another thing is that driver pushes 14 amps! Better watch that
    bypassing...
     
  15. whit3rd

    whit3rd Guest

    An easy one would be a low-voltage '555. Hysteresis from
    1/3 V to 2/3 V, good logic-switch output, doesn't need any external
    passives.
     
  16. D from BC

    D from BC Guest

    It's a favorite technique..but it's still an extra part that I think I
    can avoid it if I chose the right mosfet driver having about 1V of
    input hysteresis.
    I've haven't received an email from IXYS yet..

    I want a new 555 :)
    I want 2 high speed internal comparators (nS) rail to rail with no
    ties to internal resistors.
    Something like what Analog devices has...
    And..
    I want 1 fast internal RS latch.
    Maybe 5V HC type.
    And...Bonus if I can get a 1A push pull drive output up to 16V.
    Call it the Super555 :)
    D from BC
     
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