SHUTDOWN_REQ Oscillating Issue on Nvidia Jetson Orin Nano Dev Board

Issue Overview

The discussion centers around an issue with the #shutdown_req signal on a custom board using the Nvidia Jetson Orin Nano Dev board. Users report that when simulating a sudden power loss by turning off the power supply, the #shutdown_req signal oscillates for approximately 12 milliseconds. This behavior occurs despite following the power sequencing requirements outlined in the design guide.

Symptoms and Context

• Symptoms: The #shutdown_req signal oscillates when power is cut, leading to instability in the POWER_EN signal.

• Context: The issue arises during simulated sudden power loss scenarios. Users are attempting to ensure proper shutdown sequences as specified in Nvidia’s design documentation.

Hardware and Software Specifications

• Hardware: Custom board with a connection from #shutdown_req to a MOSFET gate, featuring a 100k pull-down resistor.

• Software: No specific software bugs or configurations were mentioned, but users are relying on the design guide for proper implementation.

Frequency and Impact

• Frequency: The issue appears consistently when simulating sudden power loss.

• Impact: The oscillation of the signals can lead to improper shutdown sequences, potentially causing data corruption or hardware damage.

Possible Causes

• Hardware Incompatibilities or Defects: The custom design may not align with reference designs, leading to unexpected behavior.

• Software Bugs or Conflicts: Although no specific software issues were mentioned, discrepancies between custom implementations and reference designs could cause conflicts.

• Configuration Errors: Incorrect configurations in the circuit design may lead to improper handling of the #shutdown_req signal.

• Driver Issues: If drivers are not properly configured to handle power management signals, this could result in oscillation.

• Environmental Factors: Fluctuations in power supply stability or voltage levels may contribute to signal instability.

• User Errors or Misconfigurations: Deviations from recommended design practices could lead to this issue.

Troubleshooting Steps, Solutions & Fixes

Step-by-Step Instructions

1. Verify Power Supply Stability:

   • Use an oscilloscope to check the stability of the power supply waveform during shutdown simulations.
   • Ensure that there are no unexpected fluctuations or dips in voltage.

2. Check Signal Timing Sequence:

   • Measure the timing sequence of VDD_IN, #shutdown_req, and POWER_EN.
   • Confirm that VDD_IN drops before the assertion of #shutdown_req, as required.

3. Compare with Reference Design:

   • Obtain reference designs from Nvidia and compare your custom board’s layout and connections with those provided.
   • Pay special attention to how the power-button micro-controller is implemented in reference designs.

4. Inspect Pull-Up Resistors and Capacitors:

   • Ensure that pull-up resistors (4.7k) are correctly placed and functioning.
   • Verify that sufficient capacitance is present on power lines to smooth out voltage drops.

5. Latch POWER_EN Signal Appropriately:

   • Implement a mechanism to hold the POWER_EN signal low for more than 10ms after the assertion of #shutdown_req, especially before VDD_IN drops below 3V.
   • This is crucial as per user discussions indicating that this timing helps stabilize the shutdown sequence.

Commands and Procedures

• To measure signals:

  # Use an oscilloscope with appropriate probes
  oscilloscope.set_timebase(10ms/div)
  oscilloscope.measure('VDD_IN', 'SHUTDOWN_REQ', 'POWER_EN')
  

Potential Fixes or Workarounds

• If oscillation persists, consider redesigning parts of your circuit to align more closely with Nvidia’s reference designs, particularly regarding the micro-controller’s role in managing shutdown requests.

• Ensure that all components are rated for their intended functions and that there are no faulty parts causing instability.

Best Practices for Prevention

• Regularly consult Nvidia’s design guides and updates for any changes or additional recommendations regarding power management.

• Implement thorough testing protocols when designing custom boards, especially under conditions simulating sudden power loss.

Unresolved Aspects

• Further clarification from Nvidia regarding the exact timing requirements for latching signals after asserting #shutdown_req would be beneficial. Users expressed uncertainty about how long signals should be held low and whether this timing is explicitly defined in available documentation.