DP83TC812R-Q1: How does the RX internal pull down resistor in MAC end influences DP83TC812R-Q1 boot mode selection

Lei Tao Tao

Part Number: DP83TC812R-Q1
Other Parts Discussed in Thread: AM2732,

Hi,

“Normally, the output IO pull-down impedance range from 20Ω-100Ω. RGMII RD is input pin for AM2732, usually, input pin's internal pull-down resistor range at -kΩ，please double confirm.” from AM2732 FAE.

InTIDA-020047 Two-device mmWave cascade reference design，DP83TC812R-Q1 strap resistor is open or 2.49KΩ，and divide with AM2732 internal pull down resistor, it seems unreasonable the voltage on strap pin is less than 5mV to define two modes.

TIDA-020047 Schematic

DP83TC812x-Q1 TC-10 Compliant 100BASE-T1 Automotive Ethernet PHY datasheet (Rev. B)

Thanks!

over 1 year ago

0 Gerome Cacho over 1 year ago

TI__Mastermind 33965 points

Hello,

For bootstrapping, it is assumed that the only voltage on the line is driven by the DC biasing on the bootstrapping resistor network in association with the PD internal resistor of the PHY. MAC must not interfere in this biasing.

Sincerely,

Gerome

0 Lei Tao Tao over 1 year ago in reply to Gerome Cacho

Prodigy 170 points

Hi Gerome,

Understood, could you please confirm with Fleenor provided some feedback information in another thread from AM2732.

(+) AM2732-Q1: RGMII RD interface internal pull down resistor value - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

Thanks！

0 Gerome Cacho over 1 year ago in reply to Lei Tao Tao

TI__Mastermind 33965 points

Hello,

Please allow me to sync up with him.

Sincerely,

Gerome

0 Lei Tao Tao over 1 year ago in reply to Gerome Cacho

Prodigy 170 points

Hi Gerome,

-Please feel free to reach out again or provide my contact information with the other supporting team (fleenor@ti.com).

Thanks!

0 Gerome Cacho over 1 year ago in reply to Lei Tao Tao

TI__Mastermind 33965 points

Hello,

Thank you for your response.

Sincerely,

Gerome

0 Lei Tao Tao over 1 year ago in reply to Gerome Cacho

Prodigy 170 points

Hi Gerome,

If you have any conclusion，please share with us!

Thanks!

0 Gerome Cacho over 1 year ago in reply to Lei Tao Tao

TI__Mastermind 33965 points

Hi Lei,

After talking with other team, our guidance still stands. MAC will need to put PHY lines into HI-Z mode, then ramp up PHY such that its bias point does not get altered by anything other than the strap resistors.

Sincerely,

Gerome

Interface

Interface forum

DP83TC812R-Q1: How does the RX internal pull down resistor in MAC end influences DP83TC812R-Q1 boot mode selection