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LMP92066: LMP92066 device version A1 output voltage accuracy

Jan Kuhne
Prodigy 60 points
Part Number: LMP92066

Hi,

so far we've been working with LMP92066 device version A0 (marking 79AXN7U) which works just fine with excellent accuracy. Now we got  a new batch of boards where the device version as read back in register 1F is A1 (device marking 7BAX89U). There, we see an accuracy of the output voltage of just +/-50..80mV, i.e. the output voltage is 50..80mV lower or higher than the set value (in override mode. register readback verifies that the correct values are written in). So

-is there any change in programming for revision A1?

-does revision A1 even exist or is it a fake chip?

-have you seen similar behavior on revision A1?

Thanks a lot and kind regards,

Jan

  • 0
    TI__Guru 52683 points
    Hi Jan,

    Let me check with our design team to see if any changes where implemented into the device.

    I will get back to you tomorrow.

    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 60 points

    Thanks a lot Paul,

    did you already get an update?

    Br

    Jan

  • 0 in reply to Jan Kuhne
    TI__Guru 52683 points
    Hi Jan,

    I checked with our test team and the test program was updated in the time between the two lots were made, but these were minor changes and the performance did not change between them. I assume the ID register was updated to denote the change.

    So that being said, can you go into more detail about the output error? When you enter override mode, does the output error improve? If you look at the output on an oscilloscope, do you see any oscillations or instability?

    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 60 points

    Thanks Paul,

    I need to take back the statement that we read device ID A0 on the earlier devices, it was A1 there as well (however, we still can distinguish the devices by the marking on the package)

    Right now we are just using override mode. No oscillations occur. I even placed a new device on a known good older PCB (where I removed the earlier device) and the behavior is the same:

    earlier devices in override mode: measured voltage is with 5mV of the set voltage

    new devices in override mode: measured voltage is up to 50mV lower (most cases) and on several more rare occasions up to 100mV higher. This is device dependent but within one device it is repeatably stable. From a blackbox perspective I would guess that the accuracy of the reference voltage is the root cause. Tests were done mostly with a target setting of 1.96V. I haven't further checked but a quick test at 2.5V seemed to increase the delta between set and measured voltaged. I can check that on monday.

    Note that measurements are done at pins 10 & 14, so directly at the DAC's with the outputs disabled.

    In the mean time we asked our pcb manufactor to get lot codes etc from their supplier.

    Br,

    Jan

  • 0 in reply to Jan Kuhne
    TI__Guru 52683 points
    Hi Jan,

    Can you share you schematic? If you do not want to post it publicly you can also email it to frost@ti.com.

    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 60 points

    Hi Paul,

    sent it via mail. Please note that the devices with the older marking all work fine within the same schematic & PCB, just the new ones have accuracy issues. Just checked one that shows at set voltage =4 V in override mode shows 4.13V on DAC1 and 3.9V on DAC0, all measured at the DAC pins with the outputs disabled. The older parts are within 5mV accuracy, very good there.

    Br,

    Jan

  • 0 in reply to Jan Kuhne
    Prodigy 60 points
    Hi Paul,

    one additional finding: on the new devices, the BURN_CT register (adress 0x40) readback yields 85, although those are new devices that haven't seen a burn cycle at our place before. On the older devices this has been always 0. This is now confirmed on several old and new devices. Also on the new devices there is already some content inside e.g. the DEL0 register (readback 170) - this is supposed to read back 0 for a brand new device, correct?

    Br
    Jan
  • 0 in reply to Jan Kuhne
    TI__Guru 52683 points
    Hi Jan,

    Your schematic looks fine (as expected, as you have not had issues with the previous builds). I am working with our planning team to verify that the history of this new lot.

    Can you verify if there are any build issues with these new board? Perhaps there are cold/unflowed solder joints? Does replacing the device or reflowing the solder fix the issue?

    In addition, are you in contact with your local TI field application engineer? Perhaps they can coordinate a return of one of these units for us to verify its functionality.

    Thank,
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 60 points

    Hi Paul,

    soldering is fine. I replaced a newer device with an older one and that worked. Replacing an older one with a newer one brought the same issue as on the completely new PCB's. I informed our local TI FAE about the issue and will arrange a return of one of the devices.

    Br,

    Jan

  • 0 in reply to Jan Kuhne
    TI__Guru 52683 points
    Hi Jan,

    I will close this thread for now, if you have any trouble with the return, please email me directly: frost@ti.com

    Thanks,
    Paul