I have the circuit below using the MCP23018 I/O controller which is always powered. The issue I'm having is that the signal USBC_RST_N controls the reset line of a PCIE-USB IC which has the ability to lose power momentarily. When the power is lost to this IC I need the USBC_RST_N signal to be pulled low until the I/O controller has the time to release the signal and pull it high again.

If the USBC_RST_N isn't pulled low before power to the PCIE-USB IC is restored then the device will not function properly and trigger a fault.

This has to be backwards compatible so I have to find a hardware solution to handle this scenario. I was thinking some type of latch circuitry would do the job but I can't seem to put something together that will work as needed. I'm hoping another set of eyes will help me see what I'm missing.

enter image description here

  • \$\begingroup\$ Is the picture related? There is no USBC_RST_N signal in the picture? \$\endgroup\$
    – Justme
    Sep 30 '20 at 16:20
  • \$\begingroup\$ @Justme I fixed it. I put an old screenshot by accident. \$\endgroup\$ Sep 30 '20 at 16:38
  • \$\begingroup\$ pull down resistor at your critical signal + a power management IC (or reset + some self build switch)? \$\endgroup\$
    – schnedan
    Sep 30 '20 at 17:33

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