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F28335 suddenly disconnects from the CCS v3.3

Javier Gonzalez
Prodigy 30 points

Hi. im working with the F28335 on a Photovoltaic application 

im using the ADC to sense voltage and current and PWM to control the Duty ratio

now im changing the duty ratio and it seems that in some point my DSP fails and disconnects from the CCS and i have to close all and start again.

i think that is because when i change the duty ratio i get many spikes in my voltage signal and i see that this spikes reach negative values and might reach more than 3 volts on the ADC

would this affect to the performance of the ADC and the DSP? how can i make it ignore this noise from the sensors (if that is the case)

  • 0
    TI__Guru 57255 points

    Javier,

    Whether or not the spikes are causing the issue will depend on the amount of time the spike occurs during and the amplitude of the spike.  Note that the ADC will have some internal clamping diodes, so in most cases this will not cause any problem.  If spikes will be common it may be a good idea to put external clamping diodes on the offending ADC pins.

    However, I don't think this is your issue.  Most likely this is a device reset issue or an issue with JTAG.  Can you probe the XRSn pin under the circumstances of the disconnect? 

    If XRSn goes low the device went into reset (a power supply brownout is one potential). 

    ---

    If XRSn doesn't go low, I'd suspect noise or issues due to emulator isolation (or lack of it).

    1. Make sure that TRSTn has an adequate pull-down.  (2.2k is what is generally suggested, but ~1.5k is also adequate)
    2. What emulator are you using?  Is the board ground isolated from the computer ground (ie is the emulator isolated)?
    3. Check the layout to make sure noise is minimized. 
    4. Potentially shield the system so that EMI is reduced.


    Thank you,
    Brett