• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 165 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.

TPS3840: Device not functional after a few power-ups

Bruno Andrade
Intellectual 530 points
Part Number: TPS3840

Tool/software:

Hi,

I have this protection circuit for reverse polarity and battery undervoltage:

It worked fine for 6 or 7 times that I powered up with my PSU at 7.2v. Circuit was cutting just fine when voltage was going down at about 4.9v, and re-enabling the mosfet at around 5.1v, as expected.

But I noticed a peak current of more than 2A for probably a few milliseconds right after powering-up the board, current after that was 200uA all the time with all the board. I do have almost 100uF of ceramic capacitance. But it's not clear to me why this would be a problem, since this FET handles much higher currents.

What I observe now is that the RESET pin of the TPS3840 does not go low anymore, stays at exactly the voltage on VDD, and the current consumption varies with the voltage now.

Could you help to identify what could be wrong? BATT comes from the battery.

Thank you very much

  • 0
    TI__Genius 9880 points

    Hi Bruno,

    Thanks for your question. First I would like to highlight that we do have supervisor that can directly connect and monitor battery rail(12V/24V/48V). And since you need UV monitoring, I would definitely recommend checking TPS3842, it's a smaller package than TPS3840, VDD SENSE, and RESET pin can go up to 42V, and it has still nano current consumption like TPS3840.

    Could you please answer below question so I can better assist you? 

    1)  What is your Battery voltage?

    2) Do you have resistor divider at sense pin? 

    - Vdd can only go up to 10V, and according to your schematic you are directly connecting to the battery rail. If you connected directly to batter rail, with peak current 2A, I think it might be damaged.

    Best,

    Sila 

  • 0 in reply to Sila Atalar
    Intellectual 530 points

    Hi Sila,

    1 - battery voltage during the tests were 7.2v, but I varied to 4.5 to 7.5 to test the cutoff circuit.

    2 - No, there is no voltage divider. What exactly could be damaged with 2A peak current, the FETs or the TPS3840?

  • 0 in reply to Bruno Andrade
    TI__Genius 9880 points

    Hi Bruno,

    thanks for clarifying my questions. 

    What is the event that the board experienced the 2A current? Was it a short or was is it expected behavior? 

    Is there anyway you can send me an oscilloscope picture so that I can share this with my team? 

    Thanks,

    Sila Atalar

  • 0 in reply to Sila Atalar
    Intellectual 530 points

    Hi Sila,

    I haven't calculated the exact initial current that is expected because of the capacitance, but it is somehow expected.

    Unfortunately I don't have an oscilloscope capture as of now.

    What I don't understand is the relationship with this in-rush current (or even if it was a real short) with the damage to the TPS device, the TPS is not in series with the circuit. Do you understand what could be the issue?

    Thank you

  • 0 in reply to Bruno Andrade
    TI__Genius 9880 points

    Hi Bruno, I will need to check with our design team to help answering your question. 

    TPS3840PH49DBVR has push-pull output, and it's active high. Since you mentioned the reset was following VDD, which means that the device is not asserting even SENSE voltage goes above than 4.9. 

    Can you please do the curve tracer procedure to all pins respect to ground as it highlighted in below. 

    Best, Sila 

  • 0 in reply to Sila Atalar
    Intellectual 530 points

    Hi Sila,

    It's 0.62v with positive lead of the multimeter on the GND pin (3) and the negative lead of the multimeter on pin RESET (1). Is this the correct measurement?

  • 0 in reply to Bruno Andrade
    TI__Genius 9880 points

    Hi Bruno, 

    Yes this is correct way. It seems like you measured 0.62V for the RESET pin. Can you quickly check VDD pin also? 

    Basically this is also a diode test. Testing for a diode drop between the IC's input/output pins can indicate if the associated transistor gates are blown. A lack of a diode drop suggests potential damage to the input or output stages.

    Just quickly want to clarify that diode testing alone is not a comprehensive IC test. I'm just trying to see if the IC damaged after that current spike. 

    Have you ever tested with other unit? If not, I recommend testing with a new one also. 

    Hope this helps!

    Best,

    Sila