Connect with us

Gate drive in datasheet

Discussion in 'Electronic Design' started by Tim Williams, Dec 10, 2012.

Scroll to continue with content
  1. Tim Williams

    Tim Williams Guest

    Whoa, never seen that before.
    http://www.ti.com/lit/ds/symlink/csd18501q5a.pdf
    Switching times measured at "RG = 0".

    I'd really like to have a copy of their drive circuit. I could solve a
    lot of problems with unlimited current drive and zero inductance, even if
    it's only 10V.

    Tim
     
  2. Guest

    That's because you are not familiar with the struggle to minimize ringing in circuits containing these devices. The RG refers to the value of dampingbootstrap resistance in the gate drive circuit. Since it's application specific they revised the original datasheet from RG 2R to RG 0R. The user will have to make his own determination of best RG.
    http://www.ti.com/lit/an/slpa010/slpa010.pdf
     
  3. miso

    miso Guest

    I could have cut them some slack if the idea was they used a low
    impedance driver rather than a function generator with 50 ohms
    impedance. That is, maybe they meant Rgen is low, as in Rgen!-=50. .
    However RG in the datasheet is the intrinsic gate resistance, so it can
    never be zero.
     
  4. Tim Williams

    Tim Williams Guest

    No, the driver source impedance. Internal RG is specified (0.5 to 1.5
    ohms or whatever). Presumably that's what they mean, but that still
    requires zero external impedance.

    How would you create a true zero ohm gate driver circuit?

    Tim
     
  5. Tim Williams

    Tim Williams Guest

    So if it's about ringing, why are they testing it at a clearly impractical
    condition?

    The appnote below only says: "durr, sometimes you need to slow it down
    with RG, but then it runs hotter". None of their waveforms even solve the
    problem set out in the title -- they all ring! I'm kind of embarassed by
    that whole appnote, frankly -- a component manufacturer's engineers should
    know the secret to quiet, efficient inverters by now. And it ain't
    "minimize inductance".

    At any rate, this doesn't answer my question: how do you implement a true
    zero ohm gate driver? Are they just out and out lying? I wouldn't put
    that past a manufacturer like International Rectifier, but TI?

    For one example, I've never seen an IXYS datasheet showing RG < 0.2 ohms
    or so, which happens to be around the output resistance of their driver
    chips. Makes perfect sense, and it's practical.

    Tim

    --
    Deep Friar: a very philosophical monk.
    Website: http://seventransistorlabs.com

    That's because you are not familiar with the struggle to minimize ringing
    in circuits containing these devices. The RG refers to the value of
    damping bootstrap resistance in the gate drive circuit. Since it's
    application specific they revised the original datasheet from RG 2R to RG
    0R. The user will have to make his own determination of best RG.
    http://www.ti.com/lit/an/slpa010/slpa010.pdf
     
  6. miso

    miso Guest

    No, the driver source impedance. Internal RG is specified (0.5 to 1.5
    I know that they mean driver impedance, but they should call it
    something else besides Rg, which is the intrinsic gate resistance. This
    is just a bad practice. It looks like apps and design were not coordinated.

    You can't make a true zero ohm driver because it is an analog world! ;-)
    Even your power supply has a finite impedance.
     
  7. miso

    miso Guest

    www.ti.com/lit/ml/slpa007/slpa007.pdf

    I'd have to see the layout to be sure, but it appears they depend on the
    silicide to keep the gate resistance low. It won't be zero, but this
    looks like a good scheme.
     
  8. Tim Williams

    Tim Williams Guest

    In case anyone was wondering, contacting TI was not illuminating. They
    said it simply means no external resistor was used. They didn't happen to
    mention what the driver impedance was. I take that to mean, if you see
    this figure in a datasheet, ignore it completely.

    Tim
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-