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TMS570LS1227 silicon revisions

user4837978
Prodigy 10 points
Other Parts Discussed in Thread: TMS570LS1227

Hello!

We have designed a custom board for the TMS570LS1227. We also have two different chips available: TMS570LS1227BPGE and TMS570LS1227CPGE.

After assembly of the PCB, using a rev. C device, I encountered some errors, wich made me suspect that the microcontroller is faulty (overheated during soldering, ESD damage).  The nERROR pin was low, although the quartz oscillator worked. After this I replaced it with a rev. B device and it worked, the nERROR pin was also high.

I repeated the process on another board with the same results: rev. B worked, rev. C didn't. Could someone please explain the difference? I have read the silicon errata for the device and haven't found anything relevant.

Here you can find the schematic for this fairly simple board. I also would like to ask if the JTAG connection is making correct use of termination and pull up and pull down resistors.7607.Stamp_TI_2017.pdf

Thank you!

Peter

  • 0
    TI__Guru 72500 points
    The difference between rev B and rev C are described in the errata documents. There should be no issue with rev C replacing rev B from a hardware standpoint. With just a quick review of your schematic I noticed that the pullup on nPORRST was pretty weak (33K). That pin has an internal 100uA pulldown. We usually use a stronger pull on that pin, (3.3K). Do you have a "power good" signal from your regulator to connect to nPORRST?