This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F280041C: Board Bringup Issue

Part Number: TMS320F280041C

Champs,

I received a new custom board and am having some issues with getting the MCU up and running. The primary symptoms of issues are that 

a) XRSn is only rising to about 2V despite having a 4.7k Pull up resistor to 3.3V. It is not cycling periodically as if the processor is in reset. I have verified the resistor value with a multimeter.

b) There is no voltage on the 1.2V rail. Note that this is the 56 pin package which does not pinout VREGENz.

Here is what I know that are good signs:

c) The 3.3V rail going into the MCU is correct and stable on both VDDA and VDDIO.

d) The MCU does seem to be up and running to some degree as there is serial data on the TMS pin. It is not a great waveform as it goes in and out of being a good square wave.

This schematic around the MCU is mostly ported from an existing working design with a F280049C 56-pin package so it is surprising to have any issues. There have been significant layout changes and modifications to the JTAG circuit, but the data above has been collected without an emulator connected so I do not expect a major impact from that. The JTAG traces are cleanly routed and are at most a couple of inches long.

What is a good place to start to determining why XRSn is not getting to 3.3V and there is not a voltage on the VDD pins?

  • This looks to be an issue with a new sensor sending serial data before the MCU has booted to the TDI and TDO pins. This data looks to be passing through the device and coming out on the TMS pin. I'll remove the sensor and go from there.

    EDIT: Sensor has been removed. That did not resolve the situation. Replaced the pull-up on XRSn with a 2.2K and it is now at 3.3V. However, there is still no 1.2V on the VDD pins and unable to connect via cJTAG

  • Hi Kris,

    When you monitor the XRSn pin during power-up are you able to see it be released (i.e. go High) sometime after VDDIO ramps? Can you also verify that the SR_SUPPLY and t_VDDIO-RAMP specs in the device datasheet are being met on the VDDIO rail?

    Best,

    Kevin

  • Hi Kevin, 

    Thank you for your reply. Please don't close this out just yet, but it looks like it is a fab or assembly problem. There is a short to ground to the 1.2V rail on all of the boards. I'll have more information tomorrow.

  • You can go ahead and close this post out. Confirmed bad assembly job in picture below. Looks like too much solder paste on the ground pad and it leaked out.