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TMP275: TMP275

Frank Bidwell
Prodigy 110 points
Part Number: TMP275

What are the ramifications of using a 1 kOhm pull up on a 5V line driving the TMP275AIDR?  The data sheet states 3 mA maximum, but the design is working with the 1 kOhm pullup (5mA) in the lab.  The I2C bus has 8 different devices on it and the original 2.1 kOhm pull up was not meeting the 300 nS rise time in all cases so we are considering a 1 kOhm part instead.

  • 0
    TI__Mastermind 43815 points

    Frank,

    You're referring to the VOL spec for TMP275's SDA pin. This states that the pin can sink up to 3mA of current while maintaining the 0.4V max spec for a logic low. If the current demand is higher than 3mA, the TMP275 may struggle to pull the voltage below 0.4V. You'll have to compare the VIL spec of the host which is interpreting the SDA logic level when TMP275 responds. This would give you an idea of the margin for error here and possible problems. It could look like TMP275 did not ACK if the host does not interpret 0.5V, for example, as logic low. 

    The TMP275 is not capable of acting as a host, so it has no SCL driver and no corresponding SCL spec. You can run 1kohm pull-up on your SCL without harm to TMP275.

    Aside from the obvious specifications, excessive pull-ups do waste current and generate heat. If you frequently ask the TMP275 to sink 3mA, you might notice a positive temperature error from the power dissipated. 

    thanks,

    ren