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DRV8662: DRV8662 Input signal not passing through Input Capacitor

Labi Shrestha
Prodigy 50 points
Part Number: DRV8662

Hi,

I'm trying to resolve an issue with a custom circuit board using the DRV8662 chip. The circuit is a replica of the DRV8662 application circuit as well as the Eval board minus the MSP430. The input signal is passed through a 0.1uF 16V X7R 0402 capacitor as shown in the datasheet and Eval kit schematics.

I'm sending an input signal which is a 1-Vpp sine wave, but some reason it appears that the input signal is not passing through the capacitor. I only measure a 1.65V DC on the other side of the capacitor. Any reason why this could happen. The rest of the circuit works, the boost voltage is correct and the gain is correct since If I bypass the capacitor, the circuit seems to work ok.

Can you please suggest why the input signal may not propagate through the input capacitor? Here's the part number of the capacitor I used GCM155R71C104JA55D (Digikey: 490-16433-1-ND)

Your help would be greatly appreciated,

Thank You,

  • 0
    Prodigy 50 points
    Correction: When I bypass the capacitor, I'm getting a DC voltage at the output, and not seeing the input signal amplified. Boost voltage is still ok.
  • 0
    TI__Mastermind 20085 points
    Hi Labi,

    It is not very clear what is going on.
    Could you explain me your application in detail? and, Could you provide me a schematic of your application?

    Best Regards
    José Luis Figueroa
    Applications Engineer
  • 0 in reply to José Luis
    Prodigy 50 points

    Circuit Schematic is as follows: Its a copy of the DRV8662 Eval board with fixed gain set to (1,1) and boost voltage set to 65V. Its is designed to drive a piezo transducer at 60V p-p.

    The device is setup to work in unipolar mode, so IN- input line is grounded through C6. The issue I'm having is that the IN+ signal (1Vp-p with 1.5V offset) looks ok on the left side of C5, but the right side of C5 measures 60V DC. I've verified that the  capacitors are ok and also tried different capacitors. Also I'm seeing the same issue on multiple boards, so I'm having trouble understanding why this is happening.

    Labi.

  • 0 in reply to Labi Shrestha
    TI__Mastermind 20085 points
    Hi Labi,

    This behavior is very weird. The schematic seems to be correct, so this could be a problem in the layout PCB.
    Are you seeing the same problem on all your boards?

    Best Regards
    José Luis Figueroa
    Applications Engineer
  • 0 in reply to Labi Shrestha
    TI__Mastermind 20085 points
    Hi Labi,

    I haven't heard back from you. I am assuming that you were able to resolve your issue. If no, just reply this post with further information or create a new one if this was locked by time-out.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer