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AMC3336-Q1: "Locking"

Matteo Telli
Prodigy 20 points
Part Number: AMC3336-Q1
Other Parts Discussed in Thread: AMC3336

Tool/software:

Good afternoon, 

I am using AMC3336-Q1 to measure a motor controller DC input bus (range 0-1000VDC). While the motor controller is operating at 20-30% of maximum current (I_Max = 150Apk), AMC3336 "locks" up:

  • Achievable range is reported. In this case 1282.9V is reported which is equivalent to ~30,518 counts.
  • DIAG line is set to 1
  • Overvoltage trip is triggered

The only way to recover is to completely cycle power. After a power cycle, IC goes back to normal operation.

DIAG line can be set to 1 due to:

  • Power brown out
    • I took a measurement between pin 3 and 8 and at the switching frequency(40kHz) voltage is ringing between 4.3 and 2.3VDC
  • A lack of data between modulator on HV side and Digital interface on LV side of IC

Data locking is a behavior that I have never observed before on these parts.

Here is the schematic



Thank you for any assistance!

  • 0
    TI__Expert 8455 points

    Hi Matteo,

    Do you have scope shots of the input and output of this "locking" behavior you are encountering? Can you describe this behavior more? Does the data stop updating?

    To clarify I understand the scenario correctly, you have designed this circuit to measure up to 1000V and at 1282.92V you are seeing the amplifier "lock" up? Please let me know if you mean differently or if there are other instances you see this. 

    The diag pin should be high during normal operation:

    What overvoltage trip are you referring to and what has your system set the overvoltage to be? 

    Please let me know so I can better advise.

    Best regards,

    Eva

  • 0 in reply to Eva Mason
    TI__Expert 8455 points

    Hi Matteo,

    Can you also share the layout if possible? Please let me know, thank you.

    You can compare it against the layout in this linked app note. A quick test could be soldering a direct connection from pin 2 to pin 8 and see if the issue is resolved. 

    Best Practices to Attenuate AMC3301 Family Radiated Emissions EMI (Rev. A)

    Best regards,

    Eva

  • 0 in reply to Eva Mason
    Prodigy 20 points

    Hello Eva, 

    Thank you for your help and sorry for the late reply.
    We came to the same conclusion. Few days ago I realized that the trace between pin 8 and 2 of U4 was creating a loop that was susceptible to electrical noises. 

    I shorted pin 2 and 8 together and the 'locking' behavior disappeared.  

    Thank you for taking the time to work with me

  • 0 in reply to Matteo Telli
    TI__Expert 8455 points

    Hi Matteo,

    Glad to hear you were able to find the solution!

    Best regards,

    Eva