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TPS2033: Current limitation occurs beyond the datasheet threshold

mathieu peyron
Prodigy 80 points
Part Number: TPS2033

Hi community,

We are using the TPS2033D as a current limiter in an USB implementation.

The ENable pin of the TPS2033D is constantly pulled high to 3.3V as soon as the device is powered up.

As a test, we connect a variable resistive charge to the USB VBUS (5V) controlled by the chip outputs.

After power-up, we increase the output current sinked by the resistive load from 100mA to 3.5A.

According to our understanding of the datasheet contents, we expected the chip to limit current at around 2.2A (2.7A at most), but this only happened over 3A.

What did we miss in the datasheet interpretation?

Thanks in advance for your support.

Mathieu.

  • 0
    TI__Mastermind 28480 points
    Mathieu,

    Your interpretation of the specification is correct. The TPS2033D should limit the current to a max of 2.7A with a typical value of 2.2A.

    Are you certain that the installed part is the TPS2033D, not the TPS2034D?

    The reason I am asking is that they behavior you are describing is consistent with the TPS2034D and the two parts are pin for pin compatible.

    Please let
  • 0 in reply to Chuck Branch
    Prodigy 80 points

    Hi Chuck,

    Thanks. We appreciate your quick answer.

    And yes, this is what I thought at first. I re-checked the package marking and verified the chip is actually a TPS2033D (component purchased from a certified source).

    Please consider the attached oscilloscope capture describing more precisely my concern :

    YELLOW: 5V input of the TPS2033

    PINK: 5V output of the TPS2033

    ORANGE: output current of the TPS2033

    Note that the beginning of the capture is not showing a short circuit condition. It is the end of the slow ramp of sinked VBUS current we apply to the TPS2033 output by slowly manually reducing the resistive load value connected to it.

    Two markers are shown on the ORANGE plot : max current before limitation occurs (around 3.6A), and limited current value (around 2.2A).

    Once "triggered", the limitation is around 2.2A indeed (consistent with the TPS2033 datasheet), but the current limitation is triggered well beyond this threshold at first (3.6A).

    Thanks for your comments.

  • 0 in reply to mathieu peyron
    TI__Mastermind 28480 points
    Mathiew,

    I am trying to find the designer on this part to see if there is a latching circuit in the part that could explain why the part changes behavior from the first event to all subsequent events.

    It might take a few days to get back to you.

    Regards,
    Chuck
  • 0 in reply to Chuck Branch
    TI__Mastermind 28480 points
    Mathieu,

    Can you try reducing the current after the first disable event to less than the current limit and then ramp it back up again without powering down the part. This will give me some more to consider while I wait to hear back internally.

    Thanks,
    Chuck
  • 0 in reply to Chuck Branch
    Prodigy 80 points

    Hello Chuck,

    Thanks again for considering my problem.

    Here is the requested capture (BLUE: 5V input, VIOLET: 5V output, YELLOW: output current).

    The initial behaviour is confirmed.

    Mathieu.

  • 0 in reply to mathieu peyron
    TI__Mastermind 28480 points
    Mathiew,

    I was not able to find a designer who worked on the TPS2033; however, I was able to find a designer who was able to explain how the part is working.

    The part allows for a DC overshoot on the current limit before the final DC current limit value of 2.4A. The slower ramp up in current that you are performing does not look like a short circuit to the part, until the current gets ver high. If you look at figure 22 in the datasheet, it shows the shape of the current limit waveform that approximately matches the scope capture that you are seeing. The part is designed to protect from a high speed short while not being sensitive to short term transients. If you need a more accurate current limit without this behavior, I can suggest other parts that would better fit your needs.
  • 0 in reply to Chuck Branch
    Prodigy 80 points

    Thanks a lot Chuck for your efforts.

    I'm affraid this chip does not fulfill my needs then.

    I believe a few clarifying words would be welcome in the next update of the datasheet.