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about LM75 address setting

Vera Mao
Expert 5065 points


dear supporting team,

when customer need pull the address pin of LM75 to low voltage, it could be drectly pulled to GND right?  while my customer is using resistor to pull it to GND, they want to know what's the biggest resistor value they can use.  tks a lot!

  • 0
    TI__Mastermind 37620 points

    Hi Vera,

    Thank you for reaching out to us. I'll get back to you.

    Aaron

  • 0 in reply to Aaron Heng
    TI__Mastermind 37620 points
    Hi Vera,

    Yes, you can connect the address pin directly to GND, but it is a good practice to connect through a resistor to GND to prevent any catastrophic event such as system failure with large current flowing into the pin. The value of the resistor should be high enough to prevent current entering the address pin. Most likely the value is about 10kΩ or larger depend on your system power supply.

    Hope this helps.

    Aaron
  • 0 in reply to Aaron Heng
    TI__Expert 5065 points

    hi Aaron,

    thank you for the answer!

    one more question, not sure how big is the small current flowing through the address pin during normal operation, my concern is  if the resistor is too big, will it cause the logic levl on the pin changed ?  such as, if customer use Mohm level resistor, and the current is around uA, then the logic level could change from GND to high. so is there any limitation for it?

  • 0 in reply to Vera Mao
    TI__Expert 4905 points
    Hi Vera,

    Aaron will be out for a few days. To answer your question the maximum logic input current is 1uA so 10k would give a 10mV voltage drop. Logic low is dependent on the VCC as it is 0.3 * Vcc. For Vcc=3V logic low would be .9V thus 10mV gives very good noise margin. Customer could even use 100k and be ok in this case as that would leave 800mV of noise margin.

    Take care,