DP83867IR: nRESET_N signal recommendation

Koichiro Tashiro

Part Number: DP83867IR
Other Parts Discussed in Thread: TXU0104

Hi,

My customer is designing their board with Sitara AM62x and DP83867IR.
In their schematics, PHY nRESET_N signal is driven by AM62x PORz_OUT signal with TXU0104 (3.3V to 1.8V level shifter) in between.
Please see slide#1 in attachment.
PHY reset.pptx
Processor team (schematics review team) recommended to insert AND logic with pull down on nRESET_n signal as slide#2.
According to "DP83867 schematic and layout checklist" linked at section 3.2 in below document,
https://www.ti.com/jp/lit/an/snla246b/snla246b.pdf
"Pin Wise Checklist", Line#18 says there is an internal pull-up at RESET_n pin.
So adding an external pull-down seems not good idea.
3107.SLVRBN1_ DP83867_Design_Review_Checklist.xlsx

What is your recommendation for nRESET_N?

Thanks and regards,
Koichiro Tashiro

over 1 year ago

0 Hillman Lin over 1 year ago

TI__Mastermind 25955 points

HI Tashiro,

Thank you for reaching out. We don't recommend reset pin to be pull down by default because reset pin is active LOW and will bring the PHY into reset stage by default.

In case something happen on the level shifter or AND logic gate, the PHY will be automatically go to reset stage. That is why we don't recommend having a pull down resistor on the reset pin. May I ask why is pull down resistor necessary in your design?

Regards,

Hillman Lin

0 Koichiro Tashiro over 1 year ago in reply to Hillman Lin

TI__Mastermind 22945 points

Hi Hillman,

Thanks for your quick reply.

Hillman Lin said:
May I ask why is pull down resistor necessary in your design?

There was no pull down in the customer's original design.
TI schematics review team recommended to add pull down.
Let me send you their review feedback offline.

Thanks and regards,
Koichiro Tashiro

+1 Hillman Lin over 1 year ago in reply to Koichiro Tashiro

TI__Mastermind 25955 points

Hi Koichiro,

Sure, we can talk about this offline.

Regards,

Hillman Lin

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DP83867IR: nRESET_N signal recommendation