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tmdscncd28335 with TMDSDOCK28335 ac adapter problem

miguel vivert
Prodigy 40 points

hello,

whenever i connect the ac adapter to the dock, my controlcard ' s LD2 & LD3 turn on and I hear a beep. the controlcard stops functioning & I can see that the adapter dc voltage  drops to 4.5 V for a short period and it goes back to 5 V , but the card stays the same.  this doesnt happen when connecting the doc with the USB cable.

What can be going on?

 thanks.

Miguel E. Vivert Del Pino

  • 0
    Guru 192875 points

    Hi Miguel,

    Check your LDO voltage levels with both connections individually. Compare their behavior.

    I can see that the adapter dc voltage  drops to 4.5 V for a short period

    This is not a good sign. Let me know what your observations are.

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Prodigy 40 points

    hi Gautam thanks,

    the output in the LDO only seems to drop 5 mV on the external adapter. in adition, there is some hf  noise on the LDO out wich is 0.5 v peak to peak lasts 2.5us ands repeat every 10 us. the noise is only present during the time in wich the DSP is actually working and then it goes away when the DSP stops working and LD2 & LD3 turn on.  I tried a different 5v 2a adapter but i get the same result. as i said before the control card and docking station work just fine with the usb adapter connected to my laptop's usb 2.0 port.

    thaks for the help.

    Miguel E.

  • 0 in reply to miguel vivert
    Guru 192875 points

     I tried a different 5v 2a adapter but i get the same result.

    Miguel, did you check the actual output from the ac adapter. Some of them do say 5V, but they output around 6.5V. Do check the LDOs datasheets for the limits and tolerances.Though this should not be the problem, but what can make the difference is the current. Check the current drawn with both the setups using current probe. Current available from USB is very less if compared with AC adapter ie 2A.

    Regards,

    Gautam