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ADC128D818: I2C communication not possible

cafain
Mastermind 6365 points
Part Number: ADC128D818

Hi staff

There is a problem with I2C communication of ADC128D818.

The problem is......
Data sheet P8: SERIAL BUS INPUTS: The maximum value of Vin (Logical 1 Input Voltage) of SCL and SDA is 5.5V(max).

When used at V + = 3.3V, if the "H" level voltage of SCL is raised to about 3.5V, it will not respond to I2C access.
It operates stably when it is suppressed to about 3.2V.

V+=3.3V　(100kbps) pullup:1kΩ
SCL = High-Level: 3.5V communication NG
SCL = High-Level: 3.2V communication OK

Please tell me the reason why communication is NG at 3.5V (H-level) even though the SCL voltage is less than the specified 5.5V.

Communication OK: ACK (Low) is output at the 9th pulse of the address phase.
Communication NG: Returns NACK (High) at the 9th pulse of the address phase.

best regards
cafain

  • 0
    TI__Mastermind 24940 points

    Hello, 

    The device can handle an input up to 5.5V, but when V+ is set to another voltage, the pull up to use the V+ voltage. 

    When the signal level at the digital input is greater than V+ voltage, the device can begin to turn on the ESD protecting structure. the device will not be damaged but can affect normal operation. 

    Use V+ as the pull up value and do not exceed V+

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Mastermind 6365 points

    Cynthia san

    Thanks for your comment.

    In the data sheet
    [The following specifications apply for 3 VDC ≤ V+ ≤ 5.5 VDC, External VREF = 2.56 V, unless otherwise specified.

    All limits TA= TJ = 25 ° C unless otherwise specified (1) With the condition of.]


    [VIN (1) Logical 1 Input Voltage TA = TJ = TMIN to TMAX 0.7 × V+ 5.5 v]


    Because it is stipulated as
    I think that the pull-up resistor voltage works fine up to 5.5V regardless of the device power supply voltage.

    Is my idea wrong?

    regards

    cafain

  • 0 in reply to cafain
    TI__Mastermind 24940 points

    Cafain san,

    I agree that this seems misleading, but I believe the intention was to show that the analog full scale range could be larger and the digital side could use a lower logic voltage. 

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Mastermind 6365 points

    Hi,  Cynthia san

    DC Electrical Characteristics of the AD128D818 data sheet
    SERIAL BUS INPUTS: SCL and SDA clearly states VIN (Max) = 5.5V.
    If your answer is correct, then VIN (Max) = V + should be.

    Is my idea wrong?
    regards
    cafain