• State
  • Locked Locked
  • Replies 9 replies
  • Subscribers 64 subscribers
  • Views 1416 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

UCD3138 V33D slew rate and lock up

jun yin
Intellectual 875 points
Other Parts Discussed in Thread: UCD3138

Sir:

There was "minimum VDD slew rate" defined in VER.B of UCD3138's datasheet, and it was deleted in VER.C datasheet;

question 1: so there is not slew rate limit for V33D, right?  I can't find it anywhere in newest datasheet;

question 2:when we power up UCD3138's V3DD very slowly, less than 1V/Second, it locks up; we have to pull low reset pin for some time to wake it up even we have set watchdog in firmware; why it locks up and why watchdog can't wake it up?

thanks 

  • 0
    Intellectual 875 points
    by lockup, I mean that GUI can't find device, ALERT pin was low, no DPWM outputs; also UCD3138's watchdog can't reset it;
  • 0 in reply to jun yin
    TI__Expert 4970 points
    Jun Yin,
    When you see the lockup, can you tell me if you see 1.8V on the BP18 pin?
    Are you seeing this behavior with your own custom board, or can you see it on one of our open loop boards?
    Can you also measure the approximate current draw of the device? If you have an open loop board, you can apply 3.3V to the V33D pin of the device and measure the input current.
  • 0 in reply to Brandon Vonk
    Intellectual 875 points
    Hi Brandon:
    Thanks a lot for your response;
    When it's lockup, BP18 pin is 1.83V; V33D/A=3.3V; RESET pin=3.3V;
    We saw this on our product, we found about 20% failure rate during the our product function test with lockup of UCD3138; on Bench test, we tried to power up by external source, then we found it locked up;
    when it's lockup, the supply current of 3.3V is around 8.69mA; while when UCD3138 is in working state, supply current is around 70mA;

    my original questions:
    question 1: so there is not slew rate limit for V33D, right? I can't find it anywhere in newest datasheet;

    question 2:when we power up UCD3138's V3DD very slowly, less than 1V/Second, it locks up; not all UCD3138 samples locked up;
  • 0 in reply to jun yin
    Intellectual 875 points

    one more picture for V33D and BP in our application which is different from bench test; it's the start-up waveform and lockup happened;

  • 0 in reply to jun yin
    TI__Expert 4970 points

    Jun Yin,

    1) Correct. There is currently no minimum slew rate requirement for the device

    2) Still investigating...

  • 0 in reply to jun yin
    TI__Genius 9845 points
    Jun Yin,

    I see a glitch on V33D. V33D must be monotonic, otherwise it may cause problem. Please solve the glitch problem and see if the lockup problem is solved.

    Thanks,
    Zhiyuan
  • 0 in reply to Zhiyuan Hu
    Intellectual 875 points

    Zhiyuan:

    Yes, there is glitch on V33D around 2.9V, the drop is less than 0.2V; it's due to the sudden charge of BP18's capacitor;

    While according to "Fig3-3 POWER ON RESET" in datasheet, there is Tpor time delay which is around 1mS when VGH which is 2.7V is exceeded to the device comes out of reset;

    according to the waveform I provided, the glitch is far away from where the device comes out of reset; you can see that from the rise time of channel 4(V33D); why it's lockup???

    Thanks

  • 0 in reply to jun yin
    TI__Genius 9845 points
    Jun Yin:

    I can't say for sure as I don't support this device. I was just offering you a clue to look into, as it is the case for UCD90xxx devices.

    2.9V is probably where the device enters brownout. Once the device enters brownout, it cannot get out until reset. You can check data sheet about this.

    Thanks,
    Zhiyuan
  • 0 in reply to Zhiyuan Hu
    Intellectual 875 points
    Zhiyuan:
    I got your point;
    we have tried to power up UCD3138 externally with V33D=2.75V, it can't work firstly, but after pull reset pin low for some time, it can work normally; so even V33D< 2.9V, brownout flag is set, the device could still work due to V33D's above VGH(2.7V), although it's not in normal working V33D range;
    I'm confusing why POWER ON RESET can't bring device back to work, which has 1mS delay; apparently from the waveform we provided, V33D is stable and around 3.3V within 1mS after ramp-up;