DP83848K Queries

Byron Loader

Other Parts Discussed in Thread: DP83848K, DP83848J

Hi Guys,

I have recently taken over a 'working design' that has some emc issues that need resolved. It is running in RMII mode. My queries resolve around the DP83848K documentation which does not give sufficient detail to understand the existing cirucit

(1) The part suggests a 10u tantalum capacitor for PFBOUT pin. My existing design includes a ceramic capacitor. Is there a fundamental reason for using a tant? If so what are the recommended ESR for such a cap.

(2) TXD2/TXD3 are pulled up and not taken to ground. I have no issues with pulling it to ground, however, there is no explanation what pulling it low does. Some insight would be useful.

Best Regards

Byron Loader

Senior Design Engineer

over 9 years ago

0 Rob Rodrigues over 9 years ago

TI__Mastermind 19780 points

Hi Byron,

(1) The tant capacitor is specified for stability of the regulator but there is enough margin to allow low ESR ceramics to work. Another post here has a slightly longer answer but does not include an ESR range: e2e.ti.com/.../718336

(2) The RMII app note applies to all DP83848 variants. Some of the variants support SNI and are put into that mode using a pull-up strap on TXD3. While the functionality is disabled on the DP83848J/K, we recommend pulling TXD2&3 to ground(valid RMII mode for all variants) so there is no confusion.

Best Regards,

0 Byron Loader over 9 years ago in reply to Rob Rodrigues

Prodigy 140 points

Thanks Rob

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DP83848K Queries