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DP83TC814R-Q1: DP83TC814R-Q1 support for strap configuration & termination resistors

Part Number: DP83TC814R-Q1
Other Parts Discussed in Thread: DP83TC814S-Q1

Hi Team, 

For DP83TC814R-Q1, please help with following questions:

1. If we have set MAC interface selection as per strap configuration in TRM section 8.5, can we still change MAC interface using SW?

In other words, which one will have higher priority? SW or strap configuration?

2. In DP83TC814R-Q1 datasheet section 9.2.1.1 it states:

"There must be no metal running beneath the common-mode choke. CMCs can inject noise into metal beneath
them, which can affect the emissions and immunity performance of the system. Because the DP83TC814S-Q1
is a voltage mode line driver, no external termination resistors are required. The ESD shunt and MDI coupling
capacitor must be connected to ground. Ensure that the common mode termination resistors are 1% tolerance or
better to improve differential coupling."

a. Does this line in red only apply to DP83TC814S-Q1 or DP83TC814R-Q1 as well?

b. Are ESD shunt and MDI coupling still required for DP83TC814R-Q1 if external termination resistors are removed? if no termination resistor is required, why does datasheet states the tolerance at the end?

Thanks

  • Hi Henry,

    Please find my responses below.

    1. We can always change the MAC interface using software. To do this, we have to disable the default MAC interface first and then enable the MAC interface which is required.
    2. a. No external 50 ohm terminations are required for all of 812, 813, 814 family devices. These terminations as usually required for current mode drivers.
      b. The highlighted resistors above are part of Common Mode termination (1k each). This requirement comes from Open Alliance Automotive specifications. This common mode termination helps in robustness of Electromagnetic RF Immunity.

    Please let me know if you need more details.

    --
    Regards,
    Gokul.