Inverting vs NonInverting Mosfet Driver
in [Design]
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From: D from BC on 8 Feb 2010 16:01 I have some fuzzy recollection of reading to the effect that noninverting mosfet drivers are more prone to instability due to layout effects. Confirm? Just doing a quick sim in my head: With poor layout, when a noninverting mosfet driver turns on (sourcing), the signal ground pops up due to the mosfet gate capacitance (iirc called ground bounce?) then the driver sees a valid (actually invalid) '0' threshold to turn the mosfet drive off.. The driver oscillates. Is it best to use a noninverting mosfet driver in a smps design? -- D from BC British Columbia
From: Joerg on 8 Feb 2010 16:32 D from BC wrote: > I have some fuzzy recollection of reading to the effect that > noninverting mosfet drivers are more prone to instability due to layout > effects. > > Confirm? > Not affirmative :-) > Just doing a quick sim in my head: > With poor layout, when a noninverting mosfet driver turns on (sourcing), > the signal ground pops up due to the mosfet gate capacitance (iirc > called ground bounce?) then the driver sees a valid (actually invalid) > '0' threshold to turn the mosfet drive off.. The driver oscillates. > > Is it best to use a noninverting mosfet driver in a smps design? > I have used both, depending on what was needed or sometimes what Digikey had in stock. Never a problem with either. Of course I never design anything without a full ground plane. Also, most modern FET drivers have input hysteresis so it's kind of tough to get them to oscillate without deliberate and serious feedback. Which I sometimes did, in order to use them as poor man's switch mode controllers and that trick only works with the inverting kind. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 8 Feb 2010 16:43 On Mon, 8 Feb 2010 13:01:17 -0800, D from BC <myrealaddress(a)comic.com> wrote: >I have some fuzzy recollection of reading to the effect that >noninverting mosfet drivers are more prone to instability due to layout >effects. > >Confirm? > >Just doing a quick sim in my head: >With poor layout, when a noninverting mosfet driver turns on (sourcing), >the signal ground pops up due to the mosfet gate capacitance (iirc >called ground bounce?) then the driver sees a valid (actually invalid) >'0' threshold to turn the mosfet drive off.. The driver oscillates. > >Is it best to use a noninverting mosfet driver in a smps design? If the driver output feeds back into the input enough to compromise the logic levels, you're in trouble either way. John
From: legg on 8 Feb 2010 22:26 On Mon, 8 Feb 2010 13:01:17 -0800, D from BC <myrealaddress(a)comic.com> wrote: >I have some fuzzy recollection of reading to the effect that >noninverting mosfet drivers are more prone to instability due to layout >effects. > >Confirm? > >Just doing a quick sim in my head: >With poor layout, when a noninverting mosfet driver turns on (sourcing), >the signal ground pops up due to the mosfet gate capacitance (iirc >called ground bounce?) then the driver sees a valid (actually invalid) >'0' threshold to turn the mosfet drive off.. The driver oscillates. > >Is it best to use a noninverting mosfet driver in a smps design? You have to test drive any prospective part, by any mfr, in-circuit. Duals and non-inverters are more prone to misbehaviour. Low voltage logic level inputs are a mistake to be avoided, wherever possible, even with a 'ground plane'. Some parts are even sensitive to output disturbances, never mind ground bounce on the input, regardless of sales blurbs or specsmanship. For non-inversion, bypass Micrel MIC4424 parts, if you want to avoid grey hair. Similar lower-powered Maxim parts MAX4427A or Micrel TC4427 seemed OK, although I recall a lack of internal UVLO, which required vigilance. RL
From: D from BC on 9 Feb 2010 15:17
In article <mui1n5td6is5t0k7054f26bpg4u78lvkfj(a)4ax.com>, legg(a)nospam.magma.ca says... > > On Mon, 8 Feb 2010 13:01:17 -0800, D from BC <myrealaddress(a)comic.com> > wrote: > > >I have some fuzzy recollection of reading to the effect that > >noninverting mosfet drivers are more prone to instability due to layout > >effects. > > > >Confirm? > > > >Just doing a quick sim in my head: > >With poor layout, when a noninverting mosfet driver turns on (sourcing), > >the signal ground pops up due to the mosfet gate capacitance (iirc > >called ground bounce?) then the driver sees a valid (actually invalid) > >'0' threshold to turn the mosfet drive off.. The driver oscillates. > > > >Is it best to use a noninverting mosfet driver in a smps design? > > You have to test drive any prospective part, by any mfr, in-circuit. > Duals and non-inverters are more prone to misbehaviour. Low voltage Ahhhh.. :) > logic level inputs are a mistake to be avoided, wherever possible, > even with a 'ground plane'. Some parts are even sensitive to output > disturbances, never mind ground bounce on the input, regardless of > sales blurbs or specsmanship. > > For non-inversion, bypass Micrel MIC4424 parts, if you want to avoid > grey hair. Similar lower-powered Maxim parts MAX4427A or Micrel TC4427 > seemed OK, although I recall a lack of internal UVLO, which required > vigilance. > > RL INteresting. Thanks I'm using a MIC4452 non-inverting. -- D from BC British Columbia |