VOH Characteristics for Open Drain Pins on Nvidia Jetson Orin Nano

Issue Overview

Users are experiencing confusion regarding the VOH (Output High Voltage) characteristics for open drain pins on the Nvidia Jetson Orin Nano development board. The specific areas of concern include:

• Interpretation of the VOH value given in the Orin Nano Series Datasheet (Table-26)
• Understanding the reference voltage (VDD) for open drain pins
• Clarification on the IOH (Output High Current) specification
• Discrepancy between expected and documented VOH values

This issue impacts users’ ability to correctly design and implement circuits using the open drain pins on the Orin Nano board, potentially affecting signal integrity and overall system performance.

Possible Causes

1. Misinterpretation of Datasheet Specifications: Users may be misunderstanding the VOH and IOH parameters as described in the datasheet, leading to confusion about their practical implications.

2. Inconsistent Terminology: The use of "VDD" in the context of open drain pins might be causing confusion, as it’s not immediately clear whether this refers to the external pull-up voltage or an internal voltage rail.

3. Unusual Specification Method: The way VOH is specified for open drain pins (as 0.85 * VDD) is not typical and may not align with users’ expectations based on experience with other systems.

4. Potential Datasheet Error: There’s a possibility that the datasheet contains an error or lacks clarity in explaining the VOH characteristics for open drain pins.

5. Complex Pin Configuration: The Orin Nano’s pin configuration might be more complex than users anticipate, with multiple voltage domains or special considerations for open drain pins.

Troubleshooting Steps, Solutions & Fixes

1. Understand VDD Reference:

   • Confirm that VDD refers to the external pull-up voltage rail, which can be either 1.8V or 3.3V.
   • Ensure your circuit design uses the correct VDD voltage for the specific pins you’re working with.

2. Clarify IOH Interpretation:

   • Understand that IOH represents the current sourced from the pin when it’s at a logic high level.
   • Note that for open drain configurations, this current is typically much lower than 1mA during normal operation.

3. Calculate Expected VOH:

   • For a more accurate VOH calculation, use the formula: VOH = VDD – (IOH * Rpull-up)
   • Example: For VDD = 3.3V, Rpull-up = 2.2kΩ, and IOH = -1mA:
     VOH ≈ 3.3V – (0.001A * 2200Ω) ≈ 1.1V

4. Consult Official Documentation:

   • Review the latest version of the Orin Nano Series Datasheet for any updates or errata related to open drain pin specifications.
   • Check the Nvidia Developer forums or support channels for official clarifications on this issue.

5. Perform Empirical Testing:

   • Set up a test circuit with various pull-up resistor values and measure the actual VOH under different load conditions.
   • Compare your measurements with the datasheet specifications and calculated values.

6. Adjust Circuit Design:

   • If your application requires a specific VOH, choose an appropriate pull-up resistor value to achieve the desired voltage level.
   • Consider using stronger pull-up resistors (lower resistance values) if you need VOH to be closer to VDD.

7. Contact Nvidia Support:

   • If discrepancies persist between your calculations, measurements, and the datasheet specifications, reach out to Nvidia technical support for clarification.
   • Provide them with your specific use case, calculations, and any test results to get the most accurate guidance.

8. Best Practices:

   • Always design your circuits with some margin for error in VOH levels.
   • Use logic-level translators or buffers if you need precise voltage levels that the open drain configuration cannot reliably provide.
   • Document any discrepancies or unusual behavior you encounter for future reference and to share with the community.

By following these steps and understanding the nuances of open drain pin behavior on the Orin Nano, you should be able to design more reliable circuits and resolve any VOH-related issues.