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DRV2700: without AC-Coupled Single-Ended DAC Input

Part Number: DRV2700

Hello,

The customer is considering DRV2700. Customers plan to connect the output of the DAC to IN + and IN- to GND. At that time, the customer would like to connect the output of the DAC to the DRV2700's IN + without AC coupling. Is there any problem?

I am looking at Figure 33. Filtered AC Coupled Single-Ended PWM Input in the DRV2700 data sheet. When connecting IN- to GND, there is C when connecting IN- to GND. Is this also necessary in this case?

In the description of the PIN function in the data sheet, IN- was NC in CONNECTION IF UNUSED. Does this mean NC if the user does not use both IN + and IN-? Is it better to do NC without connecting to GND?

Best regards,

DDdoor

  • Hi, DDdoor,

    It is possible to use the analog inputs IN+ and IN- without AC-coupling connection. However, in that case you should add an offset around 2V in order to replace the common-mode voltage that is generated once the output and boost converter are enabled. The AC-coupling capacitors allows to use the analog input without the risk to have a negative voltage that may result in a damage of the analog input (minimum negative voltage allowed is -0.3V).

    The reason of adding a capacitor to GND when the input is not being used is to avoid any short or leakage current that may be generated by the common-mode voltage. That's why we always recommend to connect these inputs to an AC-coupling capacitor.

    Please let me know if you have additional questions or comments.

    Best regards,
    Luis Fernando Rodríguez S.

  • Hello

    Thank you for your reply.

    ・ Please tell me about the input specifications when using AC coupling.
    Since the minimum of the rated voltage is -0.3V, do you recognize that the sine wave before AC coupling should be less than 0.6Vpp?
    Or is it biased and can it be input over a wider range?


    ・In the description of the PIN function in the data sheet,
    Should I interpret "Connection if unused" as NC when not using both IN + and IN-?
    (When using single end, I want to know whether to use NC or connect to GND)

    Best regards,
    DDdoor

  • Hi, DDdoor,

    1.- When using an AC coupling, the analog inputs is biased. And, as you mentioned, it allows a wider voltage range. You should consider the mid point as 2V in AC-coupling mode. This will allow to use a higher signal without risk to damage the device.

    2.- When an analog input (IN+ or IN-) is not used, you should connect it to a capacitor to ground as shown in figure 33 of datasheet ( http://www.ti.com/lit/ds/symlink/drv2700.pdf#page=21 ):

    Best regards,
    Luis Fernando Rodríguez S.

  • Hello Luis Fernando Rodríguez S,

    The customer is checking to see if the drv2700 can successfully drive the desired piezo. Therefore, page 14 of the data sheet, Figure 23. Maximum Frequency versus Maximum Voltage for Different Load Capacitances is confirmed.
    As a use case, the frequency is 500 Hz, the voltage is 93 V to 105 V,
    Piezo capacitance is 0.18 uF,
    It looks like it is located in a subtle place in the figure.

    Is it possible to operate with DRV2700?

    Best regards,

    DDdoor

  • Hi, DDdoor,

    Yes, the piezo actuator can be supported by our DRV2700.

    The limit point in the graph related to 0.18uF (180nF) would be placed at 750Hz. So, your piezo capacitance would be acceptable at 500Hz.

    Best regards,
    Luis Fernando Rodríguez S.

  • Hello Luis Fernando Rodríguez S.,

    Thank you for your reply.

    The customer is considering input of DC and sine wave using DRV2700. As the circuit, refer to the data sheet, 9.2.4 DC-Coupled Reference Input Application on page 23, Figure 35. DC-Coupled Referenced Input circuit. When confirmed by simulation, the result seems to be reversed. Negative voltage is not applied to the piezo actuator to be used. Is it correct to invert? Attach TINA TI data.

    Best regards,

    DDdoorDRV2700.tsc

  • Hi, DDdoor,

    Thank you for the information that you provided.

    I took a look at the attached file but the input doesn't seem to be inverted. Vin_diff is in phase with the Vout_diff. Could you provide more details about your question on this?

    Thank you.

    Best regards,
    Luis Fernando Rodríguez S.

  • Hi, DDdoor,

    Do you have a feedback on this? Could you take a look at my last question?

    Best regards,
    Luis Fernando Rodríguez S.

  • Hello Luis Fernando Rodríguez S.,

    Sorry for the lack of explanation.
    The design connects the Vout voltmeter in reverse.

    Best regards,

    DDdoor

  • Hi, DDdoor,

    Regarding the captures of the DRV2700EVM, the OUT+ must follow the IN+ input if the IN- is used as reference level.

    Could you take a look at sections 5.4.1 and 5.4.2 of the DRV2700EVM User's Guide? These sections are examples of the DC coupling mode. In both cases, OUT+ is not inverted.

    http://www.ti.com/lit/ug/slou403c/slou403c.pdf#page=17

    Please let me know if you have additional questions or comments on this.

    Best regards,
    Luis Fernando Rodríguez S.

  • Hello Luis Fernando Rodríguez S.

    Thank you for your reply.
    I checked the contents of the user guide that you taught me and found that the input and output tracked
    and that it was working correctly. However, the simulation model seems to have been inverted as shown in the attached design.
    I don't think the simulation model is correct. What do you think?

    Best regards,
    DDdoor

  • Hi, DDdoor,

    I agree. All the User's Guide pictures and results are verified and we can guarantee that it is the correct behavior. The simulation, on the other hand, seems to be inverted and it would be incorrect. Please follow the results of the User's Guide for reference and let us know if you have additional comments on this.

    Best regards,
    Luis Fernando Rodríguez S.