DP83825I: DP83825I strapping pulldowns

David Hand

Part Number: DP83825I

Fig 16 of the DP83825I datasheet shows recommended Rhi and Rlo resistors for the strapping pins. But it also shows a 9K ohm internal pulldown. It's clear why Rhi would be needed to pullup, but is Rlo really needed for pulldown?

Tables 8 and 9 list a DEFAULT value for each strapping. I assume that is the value if no external pullup or pulldown is attached. This would imply Rlo is not needed.

The eval board shows a place to put the optional pullups, but not external pulldowns (see attached ti_phy_pullups.jpg).

Can you tell me when the external Rlo would be needed for a pulldown?

over 5 years ago

0 Vikram Sharma over 5 years ago

TI__Genius 16030 points

Hi David,

External pull-down resitance is not required for 825's strap application.

Regards,

Vikram

0 David Hand over 5 years ago in reply to Vikram Sharma

Intellectual 915 points

Hello Vikram,

Thanks for the help.

Could you elaborate as to why the datasheet specifies a 2.49 Kohm pulldown Rlo? Is that for a special situation?

Thanks

0 Vikram Sharma over 5 years ago in reply to David Hand

TI__Genius 16030 points

Hi David,

Rlo is not applicable for 825. It is a carry forward from products which had multi-level straps where you need a resistor divider to set a defined voltage on the pin during the strap latching period. But as all our straps in 825 are 2-level straps only so either you put an external pull up or not.

Regards,

Vikram

0 David Hand over 5 years ago in reply to Vikram Sharma

Intellectual 915 points

Vikram,

That makes sense.

Thanks for the help.

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DP83825I: DP83825I strapping pulldowns