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TCA9517: Output Impedance

Kojima, Takao
Intellectual 1095 points
Part Number: TCA9517


Hello Team,

Our customer is considering to connect some control signals by 50cm wires between two PCIe evaluaiton boards.  The wires are driven by TCA9517 put on the boards as a signal buffer so he wants to know output impedance for TCA9517 to check signal quality. Culd you please help to clarify?

Best regards,

Kojima

  • 0
    Guru 319310 points

    I²C uses open-drain signals; the output impedances for falling and rising edges are different. On side A, typical output impedance is VOL / IOL ≈ 17 Ω; on side B, the voltage offsets makes it hard to compute a value, but it's probably similar.

  • +1
    TI__Guru* 77901 points

    Hi Kojima,

    As Clemen's pointed out, you can estimate the output impedance on A side by taking the VoL vs IoL to calculate the R. Figure 1 provides a table for the worst case (VccA=0.9V and VccB=2.7V).

    B side has a voltage offset so it can't be calculated in this way. The B side will try to hold a ~520mV offset no matter the current. The output drivers on B side should be similar to A side when we talk about fall time.

    I would recommend adding series resistors on the side that will connect through wires and also try to design the 9517 to have A side face the wiring. 

    -Bobby

  • +1 in reply to BOBBY
    TI__Intellectual 1095 points

    Clemen, Bobby,

    Thank you for the clarificaiton! It should be helpful for customer.

    Best regards,