Pull-downs on DM365 EVM

Andy Chernock

On the EVM for the DM365 they have external pull-down resistors on the Ethernet chip KSZ8001LI. However the chip provides internals pull downs on all the RXD signals.

This is a very congested part of my customers design, what is the necessity of the external pulldowns when internals are provided?

over 14 years ago

0 Tai Nguyen over 14 years ago

TI__Expert 5955 points

Hi Andy,

You are correct the chip provides internal pull downs on the RXD signals but these internal pull downs (or pull ups) are very weak. They are there so the lines do not float if they are not used. I would recommend to put external pull downs on these RXD signals.

Hope this hleps.

Thanks,

Tai

0 Andy Chernock over 14 years ago in reply to Tai Nguyen

Intellectual 740 points

Thank you for responding so quickly Tai.

But I would like to understand the purpose of the external pull-downs. I absolutely understand why the internals are weak and are there to protect from floating IO, but what "other" purpose are the external pull-downs used for?

0 Tai Nguyen over 14 years ago in reply to Andy Chernock

TI__Expert 5955 points

Hi Andy,

I think in this case these pull downs are to set the PHY address to 0 at power up/reset.

Thanks,

Tai

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Pull-downs on DM365 EVM