DP83826E: LED driver and termination resistor questions.

Glenn Andrews

Part Number: DP83826E

Hi All,

I feel really silly asking this, but I can't seem to find the answer in the data sheet.

Do the LED pins provide power to light the LED on the jack, or are they open-drain and rely on the other side of the LED being tied high through a current-limiting resistor?

Also:

There are termination resistors on the RX lines. Do you need to provide external 50 Ohm series resistors on the TX lines as well?

Do you need to tie the RX_D2 and RX_D3 lines low when using the chip in RMII mode?

Thanks

Glenn

over 5 years ago

0 Vikram Sharma over 5 years ago

TI__Genius 16030 points

Hi Glenn,

They are all good questions.

When LED pin is driving high, you can imagine it to be a 100ohms pull up to supply as the driving circuit.

When LED pin is driving low, you can imagine it to be a 100ohms pull down to ground as the driving cirucit.

Termination resistor is not required by phy. If MAC wants to put it (depending upon its driver impedance), then they can put it close to MAC as required.

Rx_D2 and RX_D3 should not be tied low.

Regards,

Vikram

0 Glenn Andrews over 5 years ago in reply to Vikram Sharma

Prodigy 160 points

Hi Vikram,

Thank you for your response. I really appreciate it

It sounds like the LED can be directly connected to the LED output pin, which can deliver 11mA of current to a 2.2V LED, correct?

Regards,

Glenn

0 Vikram Sharma over 5 years ago in reply to Glenn Andrews

TI__Genius 16030 points

Correct.

0 Glenn Andrews over 5 years ago in reply to Vikram Sharma

Prodigy 160 points

Thank you for clarifying, and for the rest of the answers. I really appreciate it.

Glenn

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DP83826E: LED driver and termination resistor questions.