--- In DynoMotion@yahoogroups.com, Tom Kerekes <tk@...> wrote:
>
> Bengt,
>
> Good point.  I noticed that also AFTER several Users had success with the wiring :}
>
> But it is probably ok.  The problem with connecting 5V signals to the 3.3V inputs is that there are ESD protection clamping diodes connected from the inputs to the 3.3V power rails.  This limits the voltage on the pin to 3.3V + one diode drop (~0.5V or 3.3+0.5=3.8V).  So if you short an input pin directly to the +5V supply (ie. through a limit switch) the input will definitely blow out.  However most 5V TTL outputs do not drive all the way to +5V.  They are only required to drive above 2.8V.  And if they do they don't usually source much current.  The protection diodes are rated at clamping a max of 100ma (although its not clear to me for how long).  I think very few MPGs would put out anything near this current above 3.8V.  If you have time you might test your MPG by connecting the output to the 3.3V rail through a 10 ohm resistor and check the voltage drop across the resistor.  I'd be curious.
>
> But to be totally safe you could add a 100 ohm series resistor.  (5V - 3.8V)/100ohms = 13ma max.
>
> Or best of all use the LVTH245 circuit you proposed.
>
> But I think you have the drive direction in the circuit wrong.  The spec says:
>
>
>
> FUNCTION TABLE
> INPUTS
> OPERATION
> OE DIR L     L     B data to A bus
>  L     H     A data to B bus
>  H     X      Isolation
>
> I think this means that with DIR grounded the chip will drive from B to A.  So either swap your A B signals or connect DIR to 3.3V.
>
> One additional minor thing is that the chip spec says:
>  
> NOTE 5: All unused control inputs of the device must be held at VCC or GND to ensure proper device operation. Refer to the TI application report,Implications of Slow or Floating CMOS Inputs
>  
> So just connect the unused inputs to ground.
>  
> Thanks!
> TK, literature number SCBA004
>
>
>
>
>
> ________________________________
> From: bsjoelund <cnc@...>
> To: DynoMotion@yahoogroups.com
> Sent: Sun, June 6, 2010 5:56:14 AM
> Subject: [DynoMotion] Re: Schematics
>
>  
> Hi Tom,
> You say MPG would be the same, all MPG's I have seen are 5V and JP6 handles 3.3V only, so how to use a 5V MPG?
> Cheers Bengt
>
> --- In DynoMotion@yahoogroups.com, Tom Kerekes <tk@> wrote:
> >
> > Bengt,
> >
> > Sorry no I don't.  I'd love to review one from you :}
> >
> > The MPG would be the same.
> >
> > Thanks
> > TK
> >
> >
> >
> >
> > ________________________________
> > From: bsjoelund <cnc@>
> > To: DynoMotion@yahoogroups.com
> > Sent: Fri, June 4, 2010 2:01:54 PM
> > Subject: [DynoMotion] Schematics
> >
> >  
> > Hi Tom,
> >
> > Looking in files section I can find a nice schematics as a pdf file for
> > Kflop - Snapamp - Brush - MPG.
> >
> > Do you have such file for Kflop - Kanalog - Brush (servo amps with +-10V) - MPG?
> >
> > Cheers Bengt
> >
>