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TPS274160: ST signal, open load, without pull-ups

Oba
Genius 17355 points
Part Number: TPS274160
Other Parts Discussed in Thread: TPS2H160-Q1, TPS272C45

Hello,

 

My customer has a question for open load condition of TPS274160.

 

The datasheet recommends to put external pull-ups on OUTx pins for open load condition.

Since they don’t need this open load detection, they are considering to remove the pull-up.

The host controller can ignore the ST low signal in this case, but they are concerning if the ST signal is chattering.

 

When not putting external pull-ups on OUTx pins, can ST signal be unstable (chattering)?

 

Regards,

Oba

  • 0
    TI__Mastermind 35015 points

    Oba-san,

    No issue removing the external pull-ups for open-load detection. The ST pin won't spuriously trigger. The way that open load detection works (in the off state) is by comparing the output voltage versus the input voltage and triggering the fault pin if the difference between the two is greater than Vol(off) in the datasheet. In the absence of the pull-up resistor, no current is being drawn by the open load comparator and therefore the ST pin will not trigger.

    Best Regards,
    Tim

  • 0 in reply to Timothy Logan
    TI__Genius 17355 points

    Hello Tim,

    Thanks for your reply.
    I'm a little bit confused.

    As you mentioned, Vol(off) is defined in the datasheet(P7) as like the below.

    But on the other hand, the below is from P22 of the datasheet.

    It says that when the voltage difference is smaller than V(ol, off), the fault is reported.
    P7 and P22 says opposite explanation.

    Which is correct ?. I feel P22 is correct. 

    And P22 mentioned about the leakage current.
    The leakage current is defined as the below.

    The sign is positive. Does it means the leakage current is always sink, not source?

    If it is always sink, without extenral pull-up, when the open load happens, OUT should go low.
    So the falut should not be reported. This is what I feel. Is this understanding correct?

    Regards,
    Oba

  • +1 in reply to Oba
    TI__Mastermind 35015 points

    Oba-san,

    Sorry for the late reply here. You are correct, P22 is the correct formula. I will put in a request to update the datasheet to correct this error.

    To clarify the leakage current and sink current numbers- the Iout(leak) number in your picture is from when DIAG_EN = 0 and open load detection is off. When DIAG_EN = 1, open load detection is off and a small amount of current is sunk INTO the output pin (we spec this as Iol(off)). In other versions of high-side switches we actually put this as negative current to signify it going into the device- so I will put in a request to change this to negative as well.

    Best Regards,
    Tim

  • 0 in reply to Timothy Logan
    TI__Genius 17355 points

    Hello,

    My customer is considering to change to TPS2H160-Q1 from TPS274160.
    Is the way of open load detection (when the swithc is off) of TPS2H160 the same as TPS274160? The below is their expectation.

    There is a leakage current on Vout which direction is "intto the pin". So if an externall pull up is not used, ST pin never goes to low.
    Is it the same?

    Regards,

    Oba

  • +1 in reply to Oba
    TI__Mastermind 35015 points

    Oba-san,

    The TPS2H160-Q1 is an automotive device made for 12V automotive systems. It does have a maximum rating up to 40V, however will not have a lot of the same industrial certifications as TPS274160. No explicit issue why it wouldn't work- just wanted to make your customer aware. If it is an industrial application, I would also recommend https://www.ti.com/product/TPS272C45 as it will actually have the pull-up integrated into the device. Going even further, https://www.ti.com/product/TPS274C65 will have the pull-up configurable via SPI (as well as a GPIO option). 

    To answer your question though, yes, the TPS2H160-Q1 has the same open-load OFF detection scheme as TPS274160 with the external pull-up.  "into the pin" means towards the output pin. I drew a red arrow below for your reference:

    To give you some more detail, the open load OFF detection has the following structure. I took this from the TPS272C45 datasheet, however it is similar to the TPS2H160-Q1 with the difference that there is no integrated pull-up:

    Please do not hesitate to let me know if you have any questions.

    Best Regards,
    Tim