Real-Time Clock Battery Protection for Nvidia Jetson Orin Nano

Issue Overview

The discussion revolves around the protection requirements for the Real-Time Clock (RTC) battery connection on a custom Nvidia Jetson Orin Nano design. Specifically, the user is concerned about reverse battery polarity protection and ESD (Electrostatic Discharge) protection for the PMIC_BBAT pin (pin #235). The user is seeking clarification on whether these protections are already integrated into the Power Management Integrated Circuit (PMIC) or if additional external protection circuits are necessary.

Possible Causes

1. Lack of integrated protection: The PMIC may not have built-in reverse polarity or ESD protection for the battery input.
2. Insufficient documentation: The datasheet for the specific PMIC (MP7960GRE-010F-Z) is not readily available, leading to uncertainty about its capabilities.
3. Potential reverse current: On-board capacitors on the module might cause reverse current, necessitating additional protection.
4. ESD vulnerability: The external pin may be susceptible to ESD damage without proper protection.

Troubleshooting Steps, Solutions & Fixes

1. Reference Design Analysis

   • Refer to the P2768_A04 schematic in DLC 6 for the pin design.
   • The PMIC used for BBAT is MP7960GRE-010F-Z.

2. Understanding the Reference Circuit

   • The reference design includes components D4, R222, and R560.
   • D4 is a diode used to block reverse current, not for battery polarity protection.
   • The resistors R222 and R560 are part of the protection circuit.

3. Battery Connection Guidelines

   • Only batteries should be connected; supercapacitors are not supported.
   • Charging is not supported by the PMIC.

4. Protection Circuit Implementation

   • Implement the reference circuit in your custom design:

     Battery -> R222 -> D4 -> PMIC_BBAT (Pin #235)
                 |
                R560
                 |
                GND
     

   • The diode D4 is necessary to prevent reverse current from on-board capacitors.
   • R222 and R560 provide additional protection and current limiting.

5. ESD Protection

   • There is no external ESD component on the module for the PMIC_BBAT pin.
   • Add ESD protection to your custom board design if ESD is a concern in your application.
   • Consider using a TVS (Transient Voltage Suppression) diode or an ESD protection IC.

6. Datasheet Acquisition

   • Contact Monolithic Power Systems directly to obtain the datasheet for MP7960GRE-010F-Z.
   • The manufacturer can provide specific details about built-in protections and recommended external circuits.

7. Best Practices

   • Always follow the reference circuit provided in the P2768_A04 schematic for custom designs.
   • Implement both reverse current protection (using D4) and ESD protection in your design.
   • Use high-quality components rated for the expected voltage and current levels.
   • Consider environmental factors that may affect the RTC battery connection and adjust protection accordingly.

8. Testing and Verification

   • After implementing the protection circuit, perform thorough testing:
     • Test reverse polarity connection to ensure no damage occurs.
     • Conduct ESD testing according to relevant standards (e.g., IEC 61000-4-2).
     • Verify RTC functionality over extended periods to ensure the protection doesn’t interfere with normal operation.

By following these steps and implementing the suggested protection measures, you can ensure a robust and reliable RTC battery connection for your custom Nvidia Jetson Orin Nano design.