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TPS2592ZA doubt due to datasheet change

Luiz Mellucci
Prodigy 210 points
Other Parts Discussed in Thread: TPS2592ZA, TPS25942A, TPS2592AA

We've developed some boards using TPS2592ZA and considering the datasheet SLVSC11B. This document says that recommended continuous output current is from 0A to 5A and the R_ILIM recommended range is from 40.2k to 162k.

This week I found out that a new datasheet was released, SLVSCU3. The parameters mentioned above were changed in this document: recommended continuous output current now is from 0A to 1.7A and R_ILIM recommended range now is from 10k to 45.3k. As it's a substantial change, I'm worried about our design, even though we've performed a lot of tests.

Some of our loads have high and large current peaks during their initialization (8A x 30ms and 5A x 100ms), but average/continuous current is less than 1.6A. Due to these peaks, we've to select a R_ILIM of 150k, which corresponds to I_OL of 5.2A and I_FASTTRIP of 8.3A.

Regarding the new limits of new datasheet, our average current is ok, but R_ILIM is above the recommended range. Resulting voltage at ILIM pin with 150k is 1.5V, well below the ILIM open resistor detect threshold (3.1V).

My question is: It's ok to use a 150k resistor at TPS2592ZA ILIM pin in order to accommodate the mentioned peaks since continuous current is within the recommended limit?

Need any additional information to evaluate this question?

Thanks

  • 0
    TI__Genius 15710 points

    Hi Luiz,

    This part falls under the Power Interface forum.  I will go ahead and move this post there.

     

    Thanks,

    Alek Kaknevicius

  • 0
    TI__Intellectual 2980 points
    Hello Luiz ,
    Yes, we have this data sheet change.
    few questions-
    what is your maximum input voltage.
    what is worst case min and max operating temperature?

    I would recommend to look at our TPS25942A devices to address you application requirements.

    Regards
    Dinesh
  • 0 in reply to Dinesh Kumar6
    Prodigy 210 points
    Hi Dinesh,

    One board maximum input voltage is 15V, the other one is 12,4V. The 12,4V one is the board with the current peaks mentioned. We can consider changing from TPS2592ZA to TPS2592AA if any advantage exists.

    The product operating temperature is from 10°C to 40°C, considering a 10°C elevation inside the case, we can say that limits are 10°C and 50°C.

    Thanks for the suggestion, but changing part is just a extreme option, as board design is practically done (we plan only component value changes from now) and project deadlines are arriving.

    Regards,
    Luiz
  • 0 in reply to Luiz Mellucci
    TI__Intellectual 2980 points
    Hi Luiz,
    Thanks for sharing the information.
    Good ... Now with TPS2592AA you can go up to 3.7A .. and if you still need more current with TPS2592AA , I can help you to use two devices in parallel to drive 7.4A load.
    Please let me know for the further question if any.

    Regards
    Dinesh
  • 0 in reply to Dinesh Kumar6
    Prodigy 210 points

    Hi Dinesh,

    Thanks for your repply.

    But I'd like to mantaing TPS2592ZA, or change it to TPS2592AA, as there's no space in project schedule to modifications like changing parts or adding one more in parallel (we don't have time to an additional prototype round).

    The continuous current our loads demand are until 1.6A, adequate to TPS2592ZA/AA. But It's necessary to use R_ILIM of 150k in order to pass some eventual peaks that are larger than 1.6x the maximum continuous current described in new datasheet. With R_ILIM of 150k, voltage on ILIM pin is well under the pin limit. 

    My question is: It's ok to use a 150k resistor at TPS2592ZA ILIM pin in order to accommodate the mentioned peaks since continuous current is within the recommended limit?

    Thanks.

  • 0 in reply to Luiz Mellucci
    TI__Intellectual 2980 points

    Hello Luiz,

    The recommended maximum RLIM resistor value can be 45.3k, so any higher value than this may put device in danger.

     for continuous load current of 1.6A, The maximum current, you can take will be about 3.29A , before the fast trip comp trips.

     Best Regards

    Dinesh

  • 0 in reply to Dinesh Kumar6
    Prodigy 210 points
    Hi Dinesh,

    It's really a big problem when a system is developed based on a datasheet and then it is updated with a significant modification. Until one or two weeks ago we were considering the boards design mature with just component value adjustments (no layout changes).

    Changing the layout of these boards would affect the schedule of a global project which is of key importance to Philips, hence would affect product time to market, which finally results in worse financial and intangible marketing results. We would be not very happy with Texas if this datasheet modificaton results in such impact.

    That's why I insist in questioning and I'm trying to fully understand the real/detailed impact of keeping design as it's now.

    Could you detail the possible consequences of using R_ILIM of 150k?

    Assuming we keep the 150k resistor, EVENTUAL peaks greater than 3.5A can damage the component?

    What kind of danger we are talking about? Instant fail? Premature fail? Reduction of expected life?

    Please, keep in mind that continuous current is always less than 1.6A.

    Best Regards,
    Luiz
  • 0 in reply to Luiz Mellucci
    TI__Intellectual 2980 points
    Hello Luiz,
    Here is my email ID..
    dinesh.kumar@ti.com, we can discuss this offline.. about the data sheet changes , why those were done.

    Regards
    Die sh
  • 0 in reply to Dinesh Kumar6
    Prodigy 210 points
    Just to close this doubt:

    I've talked with Texas. From what I've understand, the main concern about our design is that power dissipation can exceed IC maximum rating (50W) in a short-circuit fail event.

    R_ILIM = 150k => ILIM = 5.2A
    Voltage rail = 12.4V
    Power dissipated in a short to 0V = 64.5W

    For the voltage rail we are using, limit configuration for I_LIM would be around 4A.

    Is that right?
  • 0 in reply to Luiz Mellucci
    TI__Intellectual 865 points

    Hello Luiz,

    If the opearating ambient temperature of the IC is in the range if 0 to +85 degree C, then the max Pd rating of the part is 50W and with 12.4V input supply, the max current limit setting allowed will be 4A.

    If the tempeature range is from -40 to +85 C then max Pd allowed is 40W and the max current limit allowed with 12.4V input supply is 3.2A

    Regards,

    Dilip