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DRV2700EVM: noise , common mode

ELIMELECH KELLER
Prodigy 50 points
Part Number: DRV2700EVM
Other Parts Discussed in Thread: DRV2700

hello,

I have to design a very quite PZT driver DC-coupled with analog input signal , output ripple below 1mV.

I use your DRV2700EVM.

I have two issues :

  • on the output signal (between OUT+ and OUT -) when I put DC input I see that the output is not flat , it has some peaks from boost converter ,about 10 mV. 
    is there something to do with it ? 
    I think about external strong lop pass filter , but maybe there is something that I missed ...
  • current now I drive DRV2700EVM through TP7(+) and TP8(-) by DAC .
    when I connect it , the output become very noisy. It has a lot of pulses , It seems like common mode noise.
    how should I connect external DAC to DRV2700 ? 
    should I use differential DAC ? what is its common mode output ?
  • I would prefer to use single ended output (OUT+ to GND) instead of differential , but is seems very noisy(follow boost output ripple) is there a way to cancel it ?

Thanks ,

Elimelech.

  • 0
    TI__Mastermind 46035 points

    Hi Elimelech,

    Here's a thread of a similar issue. It's on a variant of this EVM but the advise should be sound: https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/683015/drv2700evm-hv500-i-have-noise

    Read through that and follow it's advise. If it doesn't fix your problem, let me know and we'll work through it.

    Thank you,

    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Prodigy 50 points

    Hello again,

    I think that it doesn't resolve my problem. 
    In that tread it is flyback topology, and I deal with different type of noise.

    In my setup there is capacitive load. 

    all the measures were taken with differential probes.

    I add some scope screenshot to clarify the problem.

    The green line is boost voltage (that I think it behaves good)

    The yellow line is (OUT+  -    OUT-)  voltage which has unwanted drops

    with zoom in on yellow line :

    (the green line here is measure after the capacitive load and it seems similar)

    can you advise ?

    thanks,

    Elimelech.

  • 0 in reply to ELIMELECH KELLER
    TI__Mastermind 46035 points

    Hi,

    To answer your question on single ended output, this device has a significant amount of common mode noise and relies on the differential output to cancel that. It wasn't intended to be used single-ended.

    Regarding the output dips, are you intending to use only DC inputs or will you be sending AC signals?

    Double check that you're following the instructions in 5.4 of the User Guide for DC input.

    Do you see these dips on the input side/output from the DAC? You may need the low-pass filter that you mentioned to remove artifacts/undesired frequencies.

    Thank you,

    Jeff McPherson