Non-stop PCIe device connection to the i.MX6

[torus1000]

Hi

In our use case, system power sometimes down in spite of pcie device power always on.
It means few current supply from PCIE_RXM/PCIE_RXP pins to the i.MX6.

Does this connection cause any damages to the i.MX6?

Can anyone help me?

[igorpadykov · Accepted solution]

Hi torus1000

yes providing externally voltages to unpowered i.MX may affect its reliability

and sect.4.2.1 Power-Up Sequence i.MX6DQ Datasheet notes:

NOTE
Ensure that there is no back voltage (leakage) from any supply on the board
towards the 3.3 V supply (for example, from the external components that
use both the 1.8 V and 3.3 V supplies).

http://www.nxp.com/docs/en/data-sheet/IMX6DQCEC.pdf

from sect.4.2 Power Supplies Requirements and Restrictions :

Any deviation from these..may result..

* Irreversible damage to the processor

Best regards
igor
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[torus1000]

Dear Igor,igorpadykov‌

I reviewed the difference between MCIMX6DL-SDP and our board then some questions came up.

According to the PCIe standard, All Transmitters shall be AC coupled such as PCIE_RXM/PCIE_RXP.

  PCIe AC coupling capacitors values
  https://community.nxp.com/thread/463277

  See p357
  http://composter.com.ua/documents/PCI_Express_Base_Specification_Revision_3.0.pdf

(Q1) Why 0 ohm resister placed at C7 and C8 instead of capacitor?

        Please see circuit diagram SPF-27417_C4.pdf on page 16.

In our board, 0.1uF cap placed on PCIE_RXM/PCIE_RXP lines, so that DC current will never leak.

(Q2) In such case Can I forget about fatal damage to the i.MX6 as I asked before?

I think coupling capacitors may be eliminated for REFCLKM/P but there was differential termination and AC coupled
in the MCIMX6DL-SDP schematics.

(Q3) Why reference clocks also AC coupled?

Thanks.

[igorpadykov]

Hi torus1000

>In our board, 0.1uF cap placed on PCIE_RXM/PCIE_RXP lines, so that DC current will never leak.

>(Q2) In such case Can I forget about fatal damage to the i.MX6 as I asked before?

yes

>(Q1)Why..(Q3) Why reference clocks also AC coupled?

please create new thread for that new questions.

Best regards
igor