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TPS1HB50-Q1: Current Limit vs. Fault State

Josef Warta
Expert 3910 points
Part Number: TPS1HB50-Q1

Hello Team, 
my customer has following question:

The B-version is specified with much higher current limit but has same Rdson as A-version. Also calculation for current limit is different.


But for current sense ratio there is only one value available?

For this application we need to detect 8 Amp. For 8Amp this means we need factor 1500 at SNS output with 5.33mA.
For 5V range it is necessary to use a 820 Ohm sense resistor.

But in a failure case SNS output is driving 4.5mA. Means this that we can measure only with a SNS output range up to 4.5mA which reduces the complete operating current range?

With an 820 Ohm sense resistor this means that a current of 6.75Amp is equal to Fault State. 
Is this true and how can we get the full 8 Ampere range for the TPS1HB50B version?

Many Thanks

Josef

  • 0
    TI__Genius 16390 points

    Hi Josef,

    This is a very interesting scenario. I think the question is when the SNS pin is at 4.5mA*820ohm = 3.7V, is it a fault or the current is 6.75A.

    If it's a fault, then it has to be overcurrent or overtemp fault.

    To see if it's overtemp fault, then customer can switch SNS1 high to detect temp and see if the temp is over the limit. To see if it's overcurrent fault - if it's auto-retry, then customer can see the ISNS voltage goes up and down every 2ms between 3.7V and max voltage (assume there's a clamp). If it's latched operation, then by switching to SNS1, the device temp should be at room temp as it's off.

    If none of the above applies (temp is normal, ISNS voltage is not going up and down for auto-retry, or temp is not at room temp for latched), then it's steady current around 6.75A.

    May I know if 8A is the normal operation condition or it's transient condition? If 8A is expected for long-term operation, the FET might hit thermal shutdown depending on the ambient temp.

    Please let me know what do you think.

    Regards,

    Yichi

  • 0 in reply to Yichi Zhang.
    Prodigy 130 points

    Hello,

    thank you for the answer. We want to activate a Heating element which has the power of 73W. We expect to have round about 6 A continuous load.

    For the Isns is my expecting correct, that the 4,5mA is not the highest output current? So is there also an output current of 5,33mA possible?

    If the 6A continuous load is to high for this component, can you propose a different one? 

    We are at the moment in finalization of our schematic and have to check, that these components are sufficient

    Thank you for the support.

    BR,

    Martin

  • 0 in reply to Martin Blinzler
    TI__Genius 16390 points

    Hi Martin,

    It's able to support sense of 8A. Please see the below graph.

    However, in your application, I think TPS1HB35 would be a better fit.

    It has a higher continuous current rating due to the lower Rdson. It can do 5A at 70 degC ambient. It can do more if the ambient is lowered.

    Also the current sense ratio is larger, so the problem you had with 1HB50 does not exist. The current sense for 8A will be 4mA, which is right below the FAULT current output.

    Please let me know if this works for you.

    Regards,

    Yichi

  • +1 in reply to Yichi Zhang.
    Prodigy 130 points

    Thank you very much for the information.

    BR, Martin