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TMP112 SCL/SDA Input Logic Levels

Hidekazu Fujikawa
Intellectual 460 points
Other Parts Discussed in Thread: PCA9306, TMP112

Hello,

Please tell me about the SCL/SDA input logic levels(VIH/VIL).

Although VIH = 0.7 at the data sheet, is it correct VIH = 3.3V + 0.7 = 4.0V when V+ = 3.3V?

My customer want to use such as the following.

V+ = 3.3V

SCL/SDA = 1.8V

Please check this is OK or not.

Thank you.

Best Regards,

H.Fujikawa

  • 0
    Intellectual 460 points
    Sorry for my wrong understanding.
    VIH can't be more than 3.6V...

    Let me once again question.
    Please tell me about the SCL/SDA input logic levels(VIH/VIL).
    Although VIH = 0.7(V+) at the data sheet, what does it mean (V+)?

    My customer want to use such as the following.
    V+ = 3.3V
    SCL/SDA = 1.8V

    Please check this is OK or not.
    Thank you.

    Best Regards,
    H.Fujikawa
  • 0 in reply to Hidekazu Fujikawa
    TI__Prodigy 215 points

    Fujikawa-san,

    The SCL/SDA bus voltage levels are dependent on the supply voltage (which may vary between 1.4V and 3.6V).  The datasheet states the minimum VIH level is 0.7(V+), meaning that the minimum acceptable voltage level is 70% of the supply voltage.  If V+ is 1.4V, the VIH(min) is 0.98V.  LIkewise, if V+ is 3.6V, the VIH(min) is 2.52V.  It also follows that the maximum VIL is 30% of the applied supply voltage.

    In this case, the supply voltage is 3.3V and the SDA/SCL voltage levels are 1.8V compatible.  Using the 0.7V VIH(min) requirement, this means the device is expecting a minimum voltage high of 2.31V.  So, this configuration will not work.  In this case, it is best to use a voltage translation device such as the PCA9306 (http://www.ti.com/product/PCA9306).  Another way to solve this problem is to configure the SDA/SCL bus as shown in Fig. 19 of the TMP112 datasheet.

    Regards,

    Manny Soltero

     

  • 0 in reply to Manny Soltero
    Intellectual 460 points
    Manny san,

    Thank you very much for your prompt reply.
    It became clear in your explanation.

    Thank you.
    Best Regards,
    H.Fujikawa