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LM2936Q-Q1: LM2936QHBMAX5.0/NOPB SD Pin

Ray Vincent Aranzaso
Mastermind 18180 points
Part Number: LM2936Q-Q1


Hi,

Good Day.

I need some information about PIN 5 of the device. The pin is left floating on the PCB and on the datasheet is written that to have the device on is possible to leave the pin floating (open). In the datasheet is also written that to have the device on the voltage on the SD pin has to be less than 0.6 V. The question is: If the pin is left floating how I can guarantee always the voltage below 0.6 V? Is it present an internal pull-down?

Please advise. Thank you very much.

Best Regards,

Ray Vincent

  • 0
    TI__Guru 50025 points

    Hi Ray,

    The SD description in the datasheet implies that there is an internal pull down. Are you referring to your customer's PCB?

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Mastermind 18180 points

    Hi Nick,

    Good Day. Would it be possible to share a part of an internal block diagram of the device, where is depicted the presence of pull-down? I would like to be sure on that point.

    Please advise. Thank you very much.

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    TI__Guru 50025 points

    Hi Ray,

    We don't have any design files for this device. The datasheet wouldn't say that leaving the pin floating enables the device by default if there wasn't an internal pull down so you can be sure that it is true.

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Mastermind 18180 points

    Hi Nick,

    Good Day. Please see below the response from our customer. Thank you very much.

    Today I performed some tests on the device and left the SD pin floating, the device works as written in the datasheet.

    I measured the voltage on the SD-pin (floating) and I found a negative voltage (around -100mV), on the datasheet is not written anything about the rating of the SD-PIN, but the "recommended operating conditions" suggest having the pin between 0V and 40V.

    Leaving the pin floating the value of the voltage is not under control but it's fixed by the internal circuit.

    Do you see any issue regarding the negative value that I measured?

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    TI__Guru 50025 points

    Hi Ray,

    Did they measure the voltage on the pin with a 10MΩ DMM? That might throw it off because the pull down current is usually on order of 10s of nA to uA range. Leaving the pin floating from the PCB perspective does not leave it floating from an electrical perspective. I don't think there's an issue with what you measured.

    Regards,

    Nick