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DRV2665: Piezo blower driver design using DRV2665RGPR

Shibin Varghese
Intellectual 835 points
Part Number: DRV2665
Other Parts Discussed in Thread: DRV2700

Hi Team,
We want to design a piezo blower driver.
Our requirements are as follows
Our input voltage is 3.7V nominal (2.8V to 4.2V).
The required output voltage is 60V AC.
The maximum continuous power of the blower is 1.2W.
The snippet from the datasheet of the blower is attached here.


We want to adjust the voltage to the piezo blower using the DAC of the MCU by voltage injunction at the FB pin. Is this [possible with this IC?.
Or can I adjust the output voltage through I2C?.
The AC drive required for the blower is 20-22KHz.
Is the IC DRV2665RGPRgood for our application?.
Please suggest one if this is not suitable for our application.
Looking forward to hearing from you.

  • 0
    TI__Mastermind 18985 points

    Hi Shinbin,

    the DRV2665 is a reasonable choice to drive this actuator. DRV2700 is a sister device to DRV2665 with no digital internals and may also be a good choice.

    However reaching 22 kHz may be difficult, depending on the capacitance of the blower. please see figure 23 from DRV2700 D/S

    If you wish to control the high voltage output by modulating the FB pin I would recommend the DRV2700 in a flyback configuration. this uses a transformer on the switch pin to step up the output voltage, and then an op-amp output that modulates the ground voltage of the lower side feedback resistor between 0 - 1.3 V. where 1.3V yields HV = 0V and 0V yields the maximum HV value.

    You could also do a simplified version on DRV2665 like this

    However, I think that it might be simplest in your case to connect the output of the DAC to the analog inputs of the DRV2665.

    Regards,

    Arthur

  • 0 in reply to Arthur Brown
    Intellectual 835 points

    Hi Arthur,
    Thank you for your reply.
    1). The chip DRV2700 is not available in Mouser or Digikey.
    2). Even when its sourcing is rectified, is it possible to operate at 22 kHz?.
    3). If such a high frequency is not possible can I use an H bridge for the same?.
               The H Bridge will be controlled by the MCU.
               The Chip DRV2700 (DRV2665 most likely due to availability) will be acting as a boost converter only.
               Is such a configuration possible with the IC?.
               I believe the voltage at the PVDD pin = BST pin = is the required adjusted voltage.
               If that configuration is possible, can I drive the entire 1.2W of the blower with this single IC?.
    4). Is the above-mentioned task possible with DRV2665 also?.
    5). Can I2C be used for adjusting the output voltage of the boost converter?.

  • 0 in reply to Shibin Varghese
    TI__Mastermind 18985 points

    Hi Shibin,

    I understand the DRV2700 is out of stock. it is our most popular Piezo driver.

    The reason for the frequency limit is because at higher frequencies the Piezo device will look like a smaller and smaller impedance, this means the boost needs to deliver much higher current to maintain the voltage, so unfortunately an external H-bridge wont solve this problem. (It is however possible to use DRV2665 as a boost converter only)

    you can however decrease the Rext value. this resistor controls the current through the boost inductor. if you use a boost inductor with a high saturation current and an appropriately sized Rext, you will be able to increase the bandwidth of you are able to drive, because the boost converter will be able to deliver more power. (please see 7.3.9 and figure 14 in the D/S)

    Yes, the amplitude can be adjusted with I2C, using the 100 bytes of FIFO memory on the chip. however the FIFO memory is limited to a fixed 8kHz sample rate, so the maximum frequency you could play back in this way is 4 kHz (thank you Nyquist)

    However since your MCU has a DAC available it seems to me the easiest way to recreate the desired waveform is to use the analog inputs? why do you not want to use this method?

    Regards,

    Arthur

  • 0 in reply to Arthur Brown
    Intellectual 835 points

    Hi Arthur,
    Thank you for your detailed response.
    The maximum continuous power of the piezo blower is 1.2W and the voltage is 40V.
    1). So the maximum current is 1.2W/40V=25mA. Is my calculation correct?.
    2). What is the maximum output current of the DRV265 IC?.
    3). I have a doubt since the applied voltage across the piezo blower can be adjusted, do I need to deliver more current to the driver?.
    4). If the IC DRV2665 can't be used can you suggest a driver or boost converter I can use in my case?.
    5). If a boost converter is available for such specification, I hope I can use an H bridge after the boost converter.
    Looking forward hearing from you

  • 0 in reply to Shibin Varghese
    TI__Mastermind 18985 points

    Hi Shibin,

    what is the capacitance of the blower? what is the application. Do you really need 40V at 22kHz? is the blower a single ended or differential? 

    The maximum current would be 40V /(1/(2*pi*f*C)) where f is the maximum frequency you need, and C is the capacitance of the blower.

    The maximum current isn't specified, because it greatly depends on capacitance, boost voltage and the REXT. 

    but from Figure 1 and figure 2 in DRV2700 D/S at 55Vboost you can deliver 25 mA before the boost voltage begins to drop (this is for 7.5k Rext). for 40V Vboost this would be a bit higher.

    If you use 5.5v supply, 6k Rext and a high saturation current boost inductor you can very likely drive this actuator. 

     Regards,

    Arthur

  • 0 in reply to Arthur Brown
    Intellectual 835 points

    Hi Arthur,
    Thank you for your reply.
    The capacitance of the bolwer is 5.4nF.
    If the maximum current is 40V /(1/(2*pi*f*C)) = 30mA at 40V.
    What should be the value of the Rext in such a case?.
    Can DRV2665 able to deliver this much current to the blower through the H bridge?.
    The positive and the negative of the blower are connected to the branches of the H Bridge as shown.

    In the circuit given, the voltage VHV is the 40V we want to generate.
    Looking forward to your responses.

  • 0 in reply to Shibin Varghese
    TI__Mastermind 18985 points

    Shibin, 

    Yes, DRV2665 will be able to drive this. please use a 5V supply and an Rext 6 - 7.5kOhms.

    I do not recommend using an external H-bridge circuit. The concern in DRV2665 is not the driver section, but the current delivering capability of the boost. - based on 5.4 nF capacitance this should not be an issue. there is nothing to gain from using an external H-bridge. Also if you where intending on driving the FETs with a square wave you will have high current spikes on the edges when the FETs turn 'on' because of the dV/dt current into the blower - this can damage the FETs

    I recommend you use DRV2665, 5V supply, 6 - 7.5 kOhm Rext, and use the analog input feature with the output from your MCUs DAC.

    Regards,

    Arthur

  • 0 in reply to Arthur Brown
    Intellectual 835 points

    Hi Arthur, 
    Thank you for your reply.
    My input is from a battery of nominal voltage 3.7V (2.8V to 4.2V).
    If 5V is compulsory for DRV2665, do I need to use a boost converter to generate a 5V for the DRV2665?
    One doubt, what is the difference between single-ended and differential blowers?.

  • +1 in reply to Shibin Varghese
    TI__Mastermind 18985 points

    Hi Shibin,

    DRV2665 is a suitable single chip solution for this blower.

    5V supply is only ideal. using the battery voltage to power DRV2665 is OK.

    Regards,

    Arthur