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DRV8424:Connect between PGND and GND with a resistor

Daisuke Higa
Genius 4315 points
Part Number: DRV8424

Hi support team.

My customer has a 100Ω connection between PGND and GND.
I'm not sure if this is the cause, but I'm having issues with multiple devices becoming corrupted.
We are currently investigating whether there are any issues with the layout, but could you please give us some advice on what kind of problems would occur if we used a resistor to separate PGND and GND?

Best regards,

Higa

  • +1
    TI__Mastermind 23421 points

    Hey Higa, 

    You're correct, using a resistor to separate PGND and GND on the DRV8424 can definitely cause problems, which might be contributing to the device corruption you're experiencing. Here's why:

    The purpose of PGND:

    • PGND stands for "power ground" and is intended for high-current motor drive circuitry.
    • It helps separate the high-frequency switching currents generated by the driver from the sensitive analog and logic circuitry connected to GND.
    • Ideally, PGND and GND should be connected together at a single point, usually close to the power supply input, to create a common ground reference.

    Problems with using a resistor:

    • Placing a resistor between PGND and GND creates a ground loop, disrupting the common ground reference.
    • This can introduce ground noise and voltage differences between PGND and GND, leading to:
      • Increased EMI: The ground loop can act as an antenna, radiating electromagnetic interference that can disrupt other nearby circuitry.
      • Voltage Offsets: The presence of a resistor between PGND and GND can create voltage offsets due to the voltage drop across the resistor when current flows through it. This can affect the performance of the gate drivers and other sensitive components that rely on a stable ground reference
      • Logic errors and data corruption: Voltage fluctuations on PGND can interfere with the sensitive analog and logic signals connected to GND, causing unpredictable behavior and data errors.
      • Motor control instability: Unstable ground reference can negatively impact the driver's ability to accurately control the motor current and position.
      • Thermal Performance: The thermal performance of the device can be compromised if the ground connections are not optimized. The use of large metal planes and multiple vias helps in heat dissipation, and a resistor in the ground path could interfere with this thermal management

    Recommendations:

    • Remove the resistor and connect PGND and GND together at a single point near the power supply input.
    • Ensure your layout minimizes ground loops by keeping high-current power traces separate from signal traces and routing GND planes effectively.
    • Consult the DRV8424 datasheet for recommendations on proper PCB layout and ground connections. Also see Best Practices for Board Layout of Motor Drivers - https://www.ti.com/lit/an/slva959b/slva959b.pdf#page=9