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C5515 Reserved Pins

A.Wilson
Intellectual 520 points
Other Parts Discussed in Thread: TMS320C5504

I have a custom pcb with a TMX320C5515AZCH12 and have largely followed the C5515 eZdsp USB Stick reference design.

On initial power up I am finding that all three LDO outputs are at 0V and hence the DSP is not powering correctly.

I am using an external 12MHz clock input on CLKIN and have DSP_LDO_ENABLE tied low to VSS to enable the DSP_LDO output.

I am currently checking chip connectivity and it may well be a pcb error but during my checking I have noticed a slight discrepancy with three of the RSV pins:

Looking at the eZdp c5515 USB Stick Schematic I note that C12 (RSV0), D14 (RSV3) and D13 (RSV6) are all tied low to VSS via zero ohm resistors which is what the datasheet suggests. That said these three resistors (R56,57 &58) are not populated on my eZdsp c5515 Usb Stick and yet it works.

Can you shed any light on why this is as it looks like it may be relevant?  Even if not I would like verification of how to connect these pins.

I have asked Spectrum Digital the same question but I would like to know TIs advice on this.

Regards, Andrew

  • 0
    TI__Expert 5261 points

    yes, there are certain pin connection you need to following in order to use the internal LDO.

    Please download the application migration-guild (from VC5505 to C5515). it should have this info.

    http://processors.wiki.ti.com/index.php?title=TMS320VC5504/05_to_TMS320C5504/05/14/15_Migration

    regards

    Wen

  • 0 in reply to Wen Li
    Intellectual 520 points

    Thanks Wen,

    The migration guides shed no light on the three pins C12 (RSV0), D14 (RSV3) and D13 (RSV6).

    I have now heard from Spectrum Digital who suggest that the C8 (CVDDRTC) must be powered or the LDO Outputs will possibly not power up.

    This sounds like it could be my problem as I power CVDDRTC from the USB LDO output!!!  I don't use the USB or RTC peripherals so this seemed like a good idea at the time........ oh well.

    Can you possibly confirm whether the LDO Outputs are reliant on CVDDRTC being powered first?  I guess this may be a question for the engineering staff as I can find no mention in the documentation of any dependence between LDO Outputs and CVDDRTC.

    Regards, Andrew.

     

  • 0 in reply to A.Wilson
    Intellectual 520 points

    I have now took the plunge and cut the connection between USB LDO Output and CVDDRTC and connected an external 1.3V supply to CVDDRTC.  The three LDO outputs have all sprung to life so it seems they are dependent on CVDDRTC in some way.

    Regards, Andrew

  • 0 in reply to A.Wilson
    TI__Expert 5261 points

    Hi Andrew;

    Here is an application notes that I created for TI internal use. It has details info about how to use internal LDO, and CVDDRTC pin requirement. It should help you.

    Again, please keep it in mind, it is our app notes, we are not reliable of any results of using this info. If you don't agree, please don't open this PDF file.

     

    Thanks and regads

    Wen Li

    hd_mig_5505_5515.pdf
  • 0 in reply to Wen Li
    Intellectual 520 points

    Thanks Wen,

    This is very useful - especially the PLL and CLKOUT code.

    Regards, Andrew.