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TCA9517-Q1: Interface with TAS5431-Q1

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Replies: 3

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Part Number: TCA9517-Q1

Hi Team, 

I wanted to double check and make sure it is acceptable to interface the B side of the TCA9517-Q1 with the TAS5431-Q1 I2C? I saw on the TCA9517-Q1 datasheet that the B side cannot be connected to a device with rise time accelerators. I do not believe that is a part of the circuit for the TAS5431-Q1 (it will just have pulls ups externally), but is there anything else I should review about the TAS5431-Q1 for hooking it up?

Thank you,

Jared

  • Hi Jared,

    You would be able to connect these two devices together. The important thing to keep in mind is the sizing of your pull up resistors. The V_OL of any device on the B side must be below 0.4 V. By changing the sizing of your resistors you are setting the I_OL of the device and can therefore adjust the V_OL of the TAS5431. However, the I_OL must not exceed 3 mA in order to guarantee the V_OL spec'd by the TAS5431.

    Best,

    Chris

  • In reply to Chris Ayoub:

    Hi Chris,

    Thank you for the reply! Isn't the TCA9517 spec'd so that in can received a low voltage of 0.3 * VCC? In this case, that would be up to 0.99V, which is much higher than the 0.4V output of the 5431..

    I agree regarding the pull up value, but as long as the pull up is greater than 1100 ohms, that should meet the 3mA spec, correct? (given that the pull up voltage is 3.3V)

    Thanks,

    Jared

  • In reply to Jared Becker:

    Hi Jared,

    The datasheet details the reason for this requirement in section 9.3.3 on page 11.

    "The B-side drivers operate from 2.7 V to 5.25 V. The output low level for this internal buffer is approximately 0.5 V, but the input voltage must be 70 mV or more below the output low level when the output internally is driven low. The higher-voltage low signal is called a buffered low. When the B-side I/O is driven low internally, the low is not recognized as a low by the input. This feature prevents a lockup condition from occurring when the input low condition is released. This type of design prevents 2 B-side ports from being connected to each other." 

    Due to this feature of the device the B-side pull down is not enabled unless the voltage goes below 0.4V. However as you pointed out this value is only a lower limit to value of the resistor. The TAS5431 specs a V_OL of 0.4V at 3mA so a higher resistance is recommended.

    Best,

    Chris