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Original question:

DRV2700: Controller chip for piezo motor

DRV2700: configuration to drive a piezo motor

Sebastian Reindl
Prodigy 155 points
Part Number: DRV2700

Hi experts.

I have already asked a question regarding the DRV before. Now I have looked more into the details and have some more questions:

First some information:

- I am using this as the motor: LEGS Linear LS15 from https://piezomotor.com/produkt/ls15/

- I have a DAC to create the control signal for the motor (0 to 5V)

- Desired motor voltage (DRV output) 0 to 45V

- Desired frequency: up to 1.200Hz

- Capacity of the motor is 680nF (not 100% sure about that)

Questions:

1. If I input a sinwave from 0 to 5V, can the DRV amplify that to the same sinwave but from 0 to 45V?

2. Is figure 22 in chapter 9.2.1 in the user manual the corresponding example to my case?

3. Since I only need positive voltage, I connect my piezo element between Out+ and ground. Out- remains unconnected?

4. Since my gain should not change, should I connect the gain inputs to Vcc and GND or to the microcontroller to keep them adjustable?

5. My motor has 4 legs that should work all independently. That means I need 4 DRVs, because Out+ and Out- is coupled?

6. If I connect the DAC to the DRV I only need to connect IN+, right? IN- remains unconnected?

Sorry for all that questions. It would be a huge support, if you could help me out.

Thanks

Sebastian

  • 0
    TI__Guru* 84915 points

    Hi, Sebastian,

    Please take a look at my responses below and let me know if you have additional comments.

    1. If I input a sinwave from 0 to 5V, can the DRV amplify that to the same sinwave but from 0 to 45V?
    Yes, it is posible due to the output linearity shown in Figures 13 & 14. These figures show the output behavior based on the input voltage and V(BST) voltage.

    2. Is figure 22 in chapter 9.2.1 in the user manual the corresponding example to my case?
    Yes, this example could be used to generate the waveform that you mentioned. However, it is recommended to add a low-pass filter as suggested in that section. Having a low-pass filter (cutoff frequency depends of your input signal) may be used to reduce the digital noise due to the digital to analog conversion.

    3. Since I only need positive voltage, I connect my piezo element between Out+ and ground. Out- remains unconnected?
    I don't see any problem on this since the device supports differential and single-ended inputs and outputs. I just recommend to take a look at the 9.2.1.3 Application Curves section of datasheet to see an example of the output signals that the DRV2700 can generate.

    4. Since my gain should not change, should I connect the gain inputs to Vcc and GND or to the microcontroller to keep them adjustable?
    You can connect them to a VCC or GND level in order to configure a fixed gain if you don't need to change it.

    5. My motor has 4 legs that should work all independently. That means I need 4 DRVs, because Out+ and Out- is coupled?
    If each leg needs of an independent voltage level, I mean if the signal waveform needs to be different than the others, you would need 4 DRVs as you mentioned. However, if you can achieve your desired voltage levels with the single-ended outputs, you may even use 2 of them.

    6. If I connect the DAC to the DRV I only need to connect IN+, right? IN- remains unconnected?
    When IN- is not being used, it must be connected to a capacitor to ground as shown in Figure 33 of datasheet.

    I hope this helps, please let me know if you need additional assistance.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Prodigy 155 points

    Dear Luis,

    thank you very much for your detailed answers!

    1. Looking at figure 13 & 14 it seems that an amplification is only possible up to 3V input. So my input signal has to be 0-3V. Or do I read the diagrams wrong?

    5. Yes, I will use single-ended outputs. But can I control Out+ and Out- independently? As I understand the manual, Out+ is always the opposite of Out-, isn´t it?

    Thank you and have a nice day!

    Sebastian

  • 0 in reply to Sebastian Reindl
    TI__Guru* 84915 points

    Hi, Sebastian,

    1. Looking at figure 13 & 14 it seems that an amplification is only possible up to 3V input. So my input signal has to be 0-3V. Or do I read the diagrams wrong?
    The figure 13 shows the behavior of the output voltage based on few variable parameters but at a fixed gain G = 40.7dB. In case of figure 14, it shows many graphs with variable gains and V(BST). I think that you may increase your input voltage range if you reduce the gain from 40.7dB to any of the other three options (28.8dB, 34.8dB, 38.4dB). For example, the graph plot in figure 14 can reach an increment until 3.5V but V(BST) = 30V in this case. If V(BST) value is increased, it may allow to have a higher voltage range in this case.

    5. Yes, I will use single-ended outputs. But can I control Out+ and Out- independently? As I understand the manual, Out+ is always the opposite of Out-, isn´t it?
    You are right. The OUT+ is always the opposite of OUT- since these are part of a fully-differential driver. They cannot be controlled independently in this device.

    I hope this makes sense. Please let me know if you have additional questions or comments on this.

    Have a good day too!!

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Prodigy 155 points

    Hi Luis.

    Thanks for your reply. Now I understand the figures. But can you tell me, how the gain respectively the input voltage is calculated? I used L = 20 × log (voltage ratio V2 / V1) in dB (V1=Vin) but that doesn´t bring the same result as in the figures.

    Thnaks!

    Sebastian

  • 0 in reply to Sebastian Reindl
    TI__Guru* 84915 points
    Hi, Sebastian,

    The calculation that you mentioned is correct. All the gains in our drivers are calculated or approached with that expression.

    In case of figures 13 and 14, I would say that the output voltage should be expressed in Vpp like the rest of the document. So, this makes me thing that the output voltage in those figures is only from one output (OUT+ or OUT-). You should consider the differential output to get a better approach to the expressed gain. I mean, you should duplicate the value of the output voltage in the figures for your calculation.

    Taking as examples the figures 11 and 12, they seem to take an input of ~2Vpp. The expression that you mentioned results in approximately the output voltage in both figures.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Prodigy 155 points

    Hello Luis.

    Thank you for your explanation. My results are now much more similar to the figures. Still there is some deviation, but that may be inaccuracy reading values from the figures or the difference between real and calculated values. Maybe I come back to this, when I have problems withe the prototype, but for now that´s ok!

    Thanks for your support!!

    Sebastian