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BOOSTXL-DRV8305EVM: The current sampling noise is very large, how to eliminate it

Annie Liu
Genius 10295 points
Part Number: BOOSTXL-DRV8305EVM

Hi Team,

The picture above is ISEN_A directly from the oscilloscope. If PWM is not given, the bias voltage should be sampled at this time, but the noise is very large at this time. Customer would like to know how to resolve this issue?

Thanks,

Annie

  • 0
    TI__Mastermind 18900 points

    Hello Annie,

    This looks like probing issues to me, but this is under the assumption that EVM works with whatever MCU or processor you're using. I say this because +/-350mV should be enough to disrupt proper sensing and commutation.

    Is your supply that's providing GND and PVDD at J3 connected to earth ground or is a floating GND? This can eliminate noise by linking the GND lead of the oscilloscope probe to the the same return path that is used by the supply (from the supply side, not the board side).

    I'd recommend to always probe with the intent of making the ground loop between the probe tip and the GND lead as short as possible, or probing at the locations that are important to what you're trying to see. What I mean by this, if you want to see the signal as it is, then we need to eliminate anything else that get introduced by layout or cable or other factors.

    So, if we want to measure the output of SOA (ISEN_A) as it is, then we need to measure at the pins of the device. For SOA is pin 16 (though probing the via on the top layer might be close enough. For the GND lead and return path, GND is pin 14 (but the bottom of C1) might be a good start. Everything else past that point is introducing noise into the system.

    The other way we can look at this is what the output signal will look like at the input of the MCU or processor that's attached to the launchpad. I'm sure you'll see that we actually have RC filter before going to the launchpad connectors. This means you could probe the output after the filter at the launch pad connector (top side of C23 should be fine) and the GND pin that goes to the launch pad which is pin 3 of J1 (or you can use the little via next to the pin)

    Try probing in different places and see if the waveform improves. If we can't get it to improve, then we'll have to talk about finding the source of the noise and if we can eliminate it (by looking at the frequency of the pulses or if they line up with other signals on the board, such as the PWM rising edge). 

    Best,

    -Cole