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DRV8343-Q1: nFault pin

John Pan
Intellectual 990 points
Part Number: DRV8343-Q1

Hi, I have two questions on nFault pin of DRV8343-Q1.

1) In DRV8343X-Q1EVM, the nFault pin is connected to 3.3V LDO with a pull-up resistor R51. I am wondering whether I can leave the pin open. If not, could I connect the nFault pin with a 5-V source from a DC-DC converter because my design doesn't have a 3.3V LDO but have a 5-V from a DC/DC converter that is used to source a MCU.

2) If DRV8343S-Q1 is used, the nFault pin is an active-low fault flag which will be low when a fault is present. My customer requests to Fault output be an active-high fault flag, which will be high with a voltage of VBB (12-V or 24V based on the battery) when a fault is present. Could you please advise how to use an external circuit to make it happen?

Thanks,

John

  • 0
    TI__Mastermind 18900 points

    Hello John,

    I am wondering whether I can leave [nFAULT] open [or use] 5-V from a DC/DC converter

    The nFAULT maximum recommended operating voltage is 5.5V and which indicates the nFAULT pin is compatible with anything below 5V logic (1.8V, 3.3V, and 5V are the typical rails). As such, you may change the pull up to use the 5V from the DC/DC converter.

    Leaving the nFAULT open means that the device will not be able to indicate that a Fault have occurred. Open drain will float the pin to an unknown voltage if the internal FET is not pulling the pin down to GND to indicate the fault (which is why open drain allows a flexible pull up voltage). 

    Fault output be an active-high fault flag 

    In general, it sounds like you are translating the 5V rail to a higher voltage (12V or 24V) and inverting the logic (active low vs. active high). These are all logic manipulations (translator and inverter). As a result, I suggest you check out the logic and translation business of TI: https://www.ti.com/logic-circuit/overview.html  I can also see you using the MCU and 2 GPIOs, one as an input for the nFAULT and one that turning into an inverted output which goes to a 5V to 12V or 24V translator.

    Feel free to go to their E2E forum and ask what combinations of parts might fix. Alternatively, I suggest you play around on the translator and logic link provided about and see if you can find any selection guides and resources, or browse what kind of parts they have as its good to do your own investigation before posting on the forums.

    Best,

    -Cole

  • 0 in reply to Cole Macias
    Intellectual 990 points

    Hi Cole,

    Thank you very much for your help.

    Best regards,

    John