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Original question:

TPS709: Why can't connect 'EN' to 'VIN' for TPS709

TPS709: TPS709

Dmitry Dmitry78
Prodigy 120 points
Part Number: TPS709

Hello. I am going to switch off EN TPS70950 via an open-drain microcontroller pin. What will be voltage on the EN TPS7095  if it is floating? Input voltage is 10-30V.

  • 0
    TI__Mastermind 23361 points

    Hi Dmitry, 

    The enable pin can be left floating to enable the device. You can use it with an open-drain microcontroller; you can pull the enable voltage down to disable the device. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 120 points

    I would like to be sure that the voltage on the floating EN pin doesn't harm the microcontroller. Is it zener voltage 6.5V ? What is the voltage on the loating EN (IN voltage 10-30V)?

  • 0 in reply to Dmitry Dmitry78
    TI__Mastermind 23361 points

    Hi Dmitry, 

    The absolute maximum voltage rating for the EN pin is up to 7V(see datasheet 6.1). When using this pin floating, the voltage will be less than 7V. 

    Regards, 

    Jason

  • 0 in reply to Jason Song
    Prodigy 120 points

    Сould you explain. It is important for connecting to a microcontroller. The floating pin EN (without any circuit) can have a potential  up to 7V,  right?  

  • 0 in reply to Dmitry Dmitry78
    TI__Mastermind 23361 points

    Hi Dmitry,

    I just confirmed that there is an internal clamp that would limit En pull-up to around 6.5V - 7V at nominal conditions. There is one thing you need to pay attention when using the open-drain microcontroller. When you set a high logic on the microcontroller, the leakage current into the open-drain output should not prevent the function of the internal weak pull-up with EN floating. Another way to explain this is that when EN floats, there is a small current charging the EN node to enable the device, and your open-drain leakage current should not have higher than the internal charging current. 

    Does this make sense?

    Regards,
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 120 points

    Thank you Jason Song. I will follow your recommendations