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DRV2700: About OUT+ and OUT-

Masanori Tachibana
Genius 5350 points
Part Number: DRV2700

Hi support team,

I have some questions about DRV2700.

1. Regarding the pins OUT+ and OUT-, how high is the absolute maximum rating of the output current?
2. Regarding the pins OUT+ and OUT-, what is the output current characteristic?
3. Regarding the pins OUT+ and OUT-, how high is the tolerance to the charges applied externally?
4. What is the behavior of the DRV2700 when large external charge is applied to the pins OUT+ and OUT-?
5. Could you teach tell me examples of protection measures to prevent from being applied the external larger charge on the pins OUT+ and OUT-?

Sincerely,
M. Tachibana

  • 0
    TI__Guru** 109075 points
    Hi Tachibana-san,

    As DRV2700 is a piezo driver, its load is mostly capacitive so it is based on output voltage more than output current (as opposed to resistive loads where current is important).
    There is some explanation on data sheet sections 9.2.1.2.8 and 9.2.1.2.10 that could help to understand the current constraints of this device.
    By external charge you mean an external drive (voltage/current) signal, right? That would not be good for the device. The output pins should only be connected to the piezo load and not other sources of voltage. If there are other drivers connected to the same load, in parallel, some mux or switch should be used so that the outputs of DRV2700 do not receive external signals.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Genius 5350 points

    Hi Salazar-san,

    Thank you for your reply.

    Our customer will connect piezo elements to pins OUT+ and OUT-.
    He would like to know the absolute maximum rating of output current in order to know how large capacitance of piezo elements can be connected.

    By the way, electric charge will be generated if some impact is applied to the piezo elements.
    So he suspects the reverse current flows to pins OUT+ and OUT-.
    Furthermore, even if the piezo elements which electric charge remains would connect to pins OUT+ and OUT-, the current will flow backward.
    Thus, he wants to know to how high is the tolerance for the reverse current.
    And he wants to know the countermeasure circuit against reverse current.

    Sincerely,
    M. Tachibana

  • 0 in reply to Masanori Tachibana
    TI__Guru** 109075 points
    Tachibana-san,

    DRV2700 was tested for piezos up to 4.7uF for the specs on data sheet. You should also consider that the higher the piezo capacitance the lower the bandwidth. What are the required signal frequencies?

    Regarding the reverse current, I'll double check on that.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    TI__Guru** 109075 points
    Tachibana-san,

    Regarding reverse current, the ESD diodes on the output stage should be able to protect the device from charge coming in from the piezo actuator due to movement or discharge.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Genius 5350 points
    Hi Salazar-san,

    I'm very sorry my late reply.

    We have asked our customer about the specification of the piezo element.
    But it seemed that he did not know the detailed specifications yet.
    So we explained to him that we might be able to give him appropriate advice if he did not understand specifications. And he has understood that.

    Once, this question will be closed.
    If detailed information and conditions come out, I will ask again.

    I have understood that the reverse current applied from the piezo element is absorbed by the surge protection diode of the output terminal and the voltage is clamped.
    However, the absolute maximum current of the surge protection diode is not specified.
    So I understand the tolerant of the reverse current is not specified.
    I think that an external freewheel diode would be applied generally if an inductive load is connected.

    Sincerely,
    M. Tachibana