[ADV7511W] VIL(max) spec of DDC I2C line of ADV7511W.

Hello,

I have a question about VIL(max) spec of DDCI2C line of ADV7511W.

About DDC I2C specification, HDMI 1.4a specification indicates that
the spec of DDC I2C requires to meat the I2C specification ver2.1.

According to I2C-bus Specification, version2.1, Section 15
VIL(max)  =  0.3VDD[V]
So when VDD=3.3V, the VIL(max) = 0.99V.

The Vil max of the DDC I2C line is 0.7V on the ADV7511W datasheet as follows:
VIL(max)  =  0.7[V]

Question:
We wants to know the reason of the difference.
Why is there a difference between the spec for DDC I2C of I2C-bus Specification version2.1 and ADV7511W datasheet?

Thank you!
Best regards.
Tamu

  • 0
    •  Analog Employees 
    •  Super User 
    on Jul 12, 2018 4:37 PM

    In I2C spec table 4, LOW level output voltage is 0 - 0.4 V.  As long as the ADV7511 DDC Vil(max) is greater than 0.4V then the ADV7511 will meet the I2C specifications.

  • Hello,

    Thank you for your reply.
    But your answer is not my expectation.
    I mean I ask the difference of VIL(max) between I2C bus spec and ADV7511W spec.

    According to I2C-bus Specification, version2.1, Section 15
    VIL(max)  =  0.3VDD[V]
    So when VDD=3.3V, the VIL(max) = 0.99V.

    The Vil max of the DDC I2C line is 0.7V on the ADV7511W datasheet as follows:
    VIL(max)  =  0.7[V]

    I mean I ask the reason of the difference.
    Why is there a difference between the spec of I2C-bus Specification version2.1 and ADV7511W datasheet?

    Thank you!
    Best regards.

  • 0
    •  Analog Employees 
    •  Super User 
    on Jul 13, 2018 7:02 PM

    Hi Tamu,

    When a specification is given as Vil(max) = 0.3 * VDD, this defines the maximum input threshold voltage acceptable for the input to interpret the signal as a low.  The 0.3 or 30% is defined by the silicon design and how the designers setup the ratios.  This does not mean the signal is will be at 0.3*VDD.  Normally a low signal voltage will be the resistor divider value created by the pullup resistor and the open drain resistance (<100 Ohms).  This will be less than 0.1 * VDD assuming the pullup is greater than 1K.

    The ADV7511W DDC Vil(max) = 0.8V (Table 1)

    The specification just indicates what it thinks the maximum input threshold voltage should be.  As long as the I2C pullup and pulldown ratios are acceptable then the I2C will work and the ADV7511W will work.

  • Hi GuenterL,

    Thank you for your reply.

    I think you mean that the ADV7511W DDC Vil(max) is 0.7V because it is defined by the silicon design and how the designers setup the ratios,
    but as long as the I2C pullup and pulldown ratios are acceptable then the I2C will work and the ADV7511W will work.

    Is my understanding correct?

    Thank you!
    Best regards.

  • 0
    •  Analog Employees 
    •  Super User 
    on Jul 19, 2018 4:09 PM

    Yes, this is correct