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DAC TLV5627 enters a weird "Locked" status

le zhang13643
Prodigy 50 points
Other Parts Discussed in Thread: TLV5627

8-bit 4-channel DAC TLV5627 is used in our product. And our product is used in field of building automation. We found that sometimes the TLV5627 in our product will enter a weird "Locked" status, that is:

Whatever CPU sends data to TLV5627 via SPI bus, the output voltage of TLV5627 remains unchanged. We also tried change the "fast/slow mode" and "power down/ normal operation", and the output voltage of TLV5627 still remains unchanged. The only way we can make TLV5627 out of "Locked" status is to power off and power on our product. (Hence power supply for TLV5627 first off, then on.)

We can gurantee that the data which CPU sends to TLV5627 is 100% correct and we strictly comply with the timing requirement of TLV5627 datasheet.

So my question is:

1. Under which circumstance will TLV5627 enter such kind of "Locked" status? Power fluctuation? Wrong data sent from CPU to TLV5627?

2. Is there any other customer who is using this DAC also facing the same/similiar situation?

Thanks a lot!!

  • 0
    Prodigy 50 points

    One more hint:

    Our product is used in a place where 380VAC motor and some powerful relays are used. Will all of these influence the DAC TLV5627 and cause it to enter the "Locked" status? If TLV5627 is in "Locked" status, what can be done to recover it without power off and power on our product?

  • 0 in reply to le zhang13643
    TI__Guru**** 180941 points

    Hi Le Zhang,

    I've not heard of this type of behavior before with the TLV5627, there may be a possibility that the relays are causing transients on either the SPI or Vcc pins that cause this strange behavior.  I'm sure all of your control signals are correct, but would you please consider sending me a scope shot of your timings as well as the basics of the schematic in your setup?  We can try running a few tests in our lab to try and reproduce your fault condition.  Does the DAC pull excessive current when it is in this 'weird locked up' state?

    For your specific questions:

    1. Under which circumstance will TLV5627 enter such kind of "Locked" status? Power fluctuation? Wrong data sent from CPU to TLV5627?   Answer - Power fluctuations could potentially cause this behavior; 'wrong' data (as in an extra clock or FS or /CS caused by transient glitch) could possibly get the TLV5627 out of sync, but that would also most like cause corrupted output data as well.

    2. Is there any other customer who is using this DAC also facing the same/similar situation?  Answer - not to the best of my knowledge, I have searched the QC records for similar situations and have found nothing that would infer this is a general issue with the TLV5627.

    Regards,

    Tom Hendrick

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Hi Tom Hendrick,

    Thank you for your reply. I don't know how to paste screen shot in TI E2E Community, so I write email to you.

    The following is excerpt from the email i sent:

    Please refer to the attached “actual timing.bmp” for our timings.

    Blue:     SCLK

    Yellow: DATA

    Green: CS

    Purple: FS.

    The SCLK is 3.2MHz. And the pin LDAC# is always low in our product.

     

    And the attached “analog output.jpg” and “MCU.jpg” are basics of the schematic in our product. If you need more information regarding schematic, do let me know.

     

    I am not clear whether “DAC will pull excessive current when it is in this 'weird locked up' state”. We will try to test this if possible.

     

    If in normal operation or clean environment, I believe the TLV5627 will work properly. So my concern is that if in tough environment, will TLV5627 work fine?

     

    Recently we tried to reproduce the issue in our lab and we did several EMC test, like ESD, EFT, Surge, etc. We once found that Surge test could cause the TLV5627 to output 0 and remain 0 whatever CPU sent to it.

    But 20 minutes later, TLV5627 recovers to normal status and works fine without power off/on our product. I think this could also give us some hints, although this is different from what is reported from site. In site, for example, I observed that after TLV5627 entered the weird status, “OUTA” output 1.2VDC and remains unchanged whatever CPU sends to TLV5627. And sometimes CPU tries to write “OUTA” as 2.2V, but the “OUTB” outputs 2.2VDC while “OUTA” remains 1.2VDC. This also confused us.

     

    If possible, could you please do some EMC related test in your lab with your development board or something? Thanks for your help.

    Best regards,

    Le Zhang

  • 0 in reply to le zhang13643
    Prodigy 50 points

    Hi Tom Hendrick,

    For this TLV5627 "Locked" status, we currently record two kinds of behavior in site:

    1. TLV5627 keeps output unchanged whatever CPU sends data to TLV5627 via SPI bus.

    2. CPU operates "OUTA", but "OUTA" remains unchanged while "OUTB" changes accordingly. (Note: we can gurantee that software has no problem and CPU does not write to the wrong channel of DAC)

    Hope these will not confuse you.

    Best regards,

    Le Zhang

  • 0 in reply to le zhang13643
    TI__Guru**** 180941 points

    Le,

    As we discussed during my visit, this problem appears to be layout related.  If you decide to revise the board at some point, please contact me and I'd be happy to review the layout.

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Tom,

    Thank you for your continuous support.