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GIO and HET toggling will produce Glitche

Karthikeyan Kasi Vishwanathan
Expert 1265 points
Other Parts Discussed in Thread: TMS570LC4357, TMS570LS0432

Hi TI,

I am using TMS570LC4357. Here I am having a problem with Toggling a HET Pin or GIO Pin to produce a PWM Signal.

I tried with both GIO Pin and HET Pin. I want a waveform of Ontime = Offtime = 200 us.

I produced the waveform using HET and also with GIO Pin. In both tries, I can achieve the Timings. No issues with timings.

But my problem is the Voltage.

Please have a look at the following scope shots.


So this 80 ns glitch actually pollutes my actuator to toggle a signal.

I want to know why this is happening?

rise, fall time are less than 12.5 ns as per the data sheet of TMS570LC4357. 

But 80 ns is considerably long time as for as my project is concern.

(Sometimes this time duration comes more than 40 us/ 50 us.)

This is really a big headache for me.


Please anybody help me to resolve this.

Regards,

Karthikeyan.K

  • 0
    TI__Genius 11645 points
    Karthikeyan,

    Could you pls let us know little more details on the interface between TMS570 I/O and your circuitry ?
  • 0 in reply to KARTHIKEYAN RAJAMANICKAM
    Prodigy 90 points
    Karthik,
    we didn't interface to any circuit. this observation is found in pure IO toggling of GIO pin or HET pin connected to Oscilloscope.
    we observed the same behaviour both in TMS570LC4357 HDK and TMS570LS0432 Launch pad boards.

    when we reduced the pin toggling frequency and CPU clock frequency the amplitude of the spikes reduces.
    can this be a problem due to crosstalk in the boards?

    regards,
    Dinesh
  • 0 in reply to Dinesh Kumar Mani
    TI__Mastermind 22715 points
    This is caused by the reflection due to the impedance mismatching at the point the scope is hooked up. First, you need to do an analysis to see if ripple cause by reflection is OK for the circuit you are going to connect.

    Thanks and regards,

    Zhaohong
  • 0 in reply to Zhaohong Zhang
    Prodigy 90 points

    Observations made further:

    1. Connecting to my circuit, the MCU HET pin is connected to MAX4533 analog switch IN pin. the spike is causing problem to my end application as we are trying to simulate digital sensor

    2. we tried adding a 1KOhm series resistor where the spike is totally smoothed out.


    what can be a right solution or suggestion to match impedance? adding series resistor to all IO and HET pins is not an acceptable solution for us.

    regards,

    dinesh