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DRV2700EVM: Configuration issue or defect ?

Niels Petter
Prodigy 20 points
Part Number: DRV2700EVM
Other Parts Discussed in Thread: DRV2700

Hi Folks,

I want to use DRV2700EVM in following setup:

  • VIN supply: J2 @ 3V3 and JP10, JP11 set to VIN
  • Single ended input (connect regulated voltage supply 0V to 3V3 @ TP7 +, TP8 GND)
  • Single ended output with TDK PowerHap 2.5G Piezo connected to Out+ / GND
  • No MSP interaction: Jumpers JP5,JP5 open
  • BST set to 83V
  • GAIN: Diffent gains tested
  • JP12 is set

When Piezo is connected there is loud accoustic noise from Piezo, the output voltage drops to 0V with spikes /Audio frequency). Another Piezo would not work either.

When I remove the Piezo and measure output voltage there is an gain depended offset voltage of e.g. 40V @ 40.7dB. Increasing input voltage slowly from 0V to 3V3 will partially work: The voltage range from 40V to 83V works as expected :-)

I wonder if I miss something ? Or what I did wrong ?

Any suggestions ?

BR

Niels

  • 0
    TI__Genius 10332 points

    Hi Niels,

    Thanks for reaching out on E2E. We have done many experiments with the TDK PowerHap series and our device is capable of driving the 2.5G piezo to its fullest ability. There is one issue with your setup.

    The DRV2700 is a fully differential amplifier, and therefore the outputs are biased at V_BST/2 in order to improve CMRR. This means when the device is shutdown (enable pulled low), the outputs will bias back to this level. In your case ~40V. You can still use a single ended input, but the piezo needs to be connects differentially across OUT+/OUT-. To use a single ended output, you could follow figure 36 in the datasheet, but we find the differential output will be best for this piezo. I've attached an oscilloscope shot of our test below.

    Setup:

    Set the boost to 70V, I believe the 2.5G is only rated for 60V.

    Provide the 3.3V input signal to IN+ through TP7, and you can either ground TP8 or remove JP_DC.

    Attach piezo across OUT+/-.

  • 0 in reply to Kelly Griffin
    Prodigy 20 points
    Hi Kelly,

    Thanks for your quick reply. Using differential voltage out solved my problem.

    BR
    Niels