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f28335 QEP input pin TTL compatible.

Nathan Chai
Prodigy 60 points
Other Parts Discussed in Thread: TMS320F28335, TMS320F28334, TMS320F28332

Hi,

I wonder if the f28335 Qep A, B and index Pin can tolerate 5v for high level?

In the eZDSP guide, it said all input are 3.3v compatible. But in the "TMS320F28335, TMS320F28334, TMS320F28332 data manual" says all digitil input are TTL compatible?

Would someone please help to clarify this?

Rgs

Nathan

 

  • 0
    TI__Expert 8500 points

    Nathan,

    No the pins are not 5V tolerant. The reference to TTL means the Vil/Vih/Vol/Voh levels are compatible to TTL. However, there is still a cap at 4.6v as defined in the absolute maximum ratings of the datasheet. If you use a clamping diode you can connect it to TTL logic. Or if you limit the current to < 2mA there is a clamp diode internally.

    Regards,
    Dave Foley

     

  • 0 in reply to David Foley
    Prodigy 60 points

    Hi Dave,

    Thanks for the reply.

    If I have a pull-up resister 10K connect to 5v, assuming that the internal clamp diode is 3v, that means the current would be (5-3)/10K = 0.2mA. Then it could satisfy the input requirement without damaging the DSP.

    Am I right?

     

    Rgs

    Nathan

     

     

     

  • 0 in reply to Nathan Chai
    TI__Expert 8500 points

    Nathan,

    Yes, putting a 10K resistor between the 5V source and the pin satisfies the current requirements of the internal clamp. I guess what might be unclear is whether your TTL Vol output will stay at a TTL level on the pin side of the resistor. The input buffer is CMOS, but there are internal pullups on most pins. I think you can turn them off on the F28335 device, so you may want to consider that.

    Regards,
    Dave Foley