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Net classes - How to connect same signal/diff class?

Former Member

Hi All,

 

I'm getting the hang of Eagle and I've gone through my schematic and setup net classes for various signal types.   I have some "power" traces I need for motor h-bridge.  For example for this I have a net class "MTRPOWER+" which is the positive voltage and I have sized the trace to carry 6 amps.   Likewise I have a "MTRPOWER-" which is the motor return also sized for 6 amps.

 

I am driving my MOSFETs with Microchip drivers and they require both the motor + and - but will carry no where near the current.  So I wanted to make two new net classes which were appropriate to route signals to these driver chips.  All seems logical but when I try to connect say the ground on my driver chip to the motor power ground which is MTRPOWER- it changes my lower level net class to match the bigger net class.

 

Then when I try to route it on the board i get this huge trace that I could of course resize but I'm wondering what is the correct way to deal with this?

 

Thanks in advance.

 

Also on the net class setup there seems to be a bunch of additional information on drills and such.  It seems that is not really needed (I hope) if you are just trying to figure out trace sizes, clearances and routing info.  Am I off base?

  • 0

    On 17/11/14 03:43, Mark Holbrook wrote:

    I am driving my MOSFETs with Microchip drivers and they require both the

    motor + and - but will carry no where near the current.  So I wanted to

    make two new net classes which were appropriate to route signals to

    these driver chips.  All seems logical but when I try to connect say the

    ground on my driver chip to the motor power ground which is MTRPOWER- it

    changes my lower level net class to match the bigger net class.

     

    You're kind of close, thinking of two net classes, but you need to go

    one step further. If the signals connecting to the drivers are going to

    have different characteristics to the ones connecting to the MOSFETs

    then they have to be different nets. If they're not different nets then

    they must be identical.

     

    Of course, that raises the question "how do I have two different nets

    that are electrically connected?"

     

    The answer to this is that you have to create a pseudo-component to link

    two nets together. The schematic symbol would be two pins end-to-end

    while the package would be two (small) SMD pads overlapping. This will

    create DRC errors but you can approve them since you know you intended

    it that way.