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DRV8662EVM

Curtis Harrison
Intellectual 260 points
Other Parts Discussed in Thread: DRV8662EVM, DRV8662

I'm attempting to use the DRV8662EVM.  Unfortunately, it either isn't delivering what the spec says it should deliver, or I'm doing something wrong.  I suspect the latter..

Anyway, I want to use the DRV8662 to amplify my Piezo Transducer to give it a 50v peak to peak waveform at 25khz.

So, to test this out, I got the DRV8662EVM and am trying to get it to do the above.

I applied 4.65vdc to the VBATT terminals.  The 'Active' light flashes.  I power off and connect my Piezo directly to the + and - pins on the OUT terminal.

Power on and active light blinks again.

Power down

I built a first order filter using the schematic in the UserGuide and connected it between my PWM and the EXTIN pins

I also removed JP2 and 3 as per the User Guide Instructions.

Power on and press the "TRIG" button 1 time to enter mode 2 which has External Signal Enabled, and Gain 0 and 1 both disabled.  LEDs have Active solid ON and both Gain LEDs off.

Apply power again and get pretty much nothing from the OUT terminals.  I would have expected a 50v amplification of my PWM waveform at 25khz, but I get noise.

I tested my input waveform with an oscilloscope.  It is accurately showing a square wave at 25khz with -3 to +3 peak to peak voltage.

I tested waveform coming out of the First Order Filter.  It's barely measurable, but is a weak sign wave at about 25khz.

I then removed the first order filter and attached my PWM signal directly to the EXTIN pins.  At this point, I DO get a visible signal, however, it is not amplified.  In fact, the signal coming out of the OUT pins is weaker than what is going into the EXTIN pins.

My Piezo has a capacitance of 2500pF.

Any ideas why the DRV8662EVM isn't amplifying my signal and BOOSTING my voltage through the piezo?  Can  the DRV8662 be used to amplify a PWM signal?

Thanks

  • 0
    TI__Expert 3791 points
    Hello Curtis,

    In summary you are trying to drive a 50Vpp 25kHz waveform using an external PWM (Mode2, with Gain0/1 = LOW). So to answer your question, yes, the DRV8662 can amplify the PWM signal when used with a Low-Pass Filter.

    Okay, so lets start by making sure the DRV8662 is operating correctly-- can you test to make sure the output signal is working using the MSP430 PWM input at different gains? Use the sample waveforms and make sure that the PWM is sent through the Low-Pass filter as described in section 3.3.1.

    Best Regards,
    Javier Palomo
  • 0 in reply to JP
    Intellectual 260 points
    I connected 3.45v to the VBatt terminals. I attached my piezo to the output terminals and attached a scope there as well. I cycled through all the modes using the pushbuttons on the evm board.

    The LEDs change to indicate the different modes,. But I see only a minor change on my scope and on the volume coming out of the piezo.

    It never gets past 1 volt. Every once in a while I see a brief flash of a waveform, but only for a fraction of a second.

    It should be noticed that I am getting my 3.45v from an Arduino Nano. I have also tried connecting the 5v from the Arduino Nano. Could it be that the Arduino Nano is not providing enough amperage to power the DRV8662EVM board? Do I need to connect directly to a battery or to a bench supply for this to work correctly?

    Thanks,
    Curtis
  • 0 in reply to Curtis Harrison
    TI__Expert 3791 points
    Curtis,

    I am not sure how much current the Arduino boards can supply, but the supply current may be the limiting factor here (Section 7.5 Electrical Characteristics: shows the avg bat current consumption).

    Try using the device connected to a power supply or battery source, because it does not sound like the input PWM signal is the issue rather the device operation.

    Best Regards,
    Javier Palomo
  • 0 in reply to JP
    Intellectual 260 points
    Looking at the user guide, the DRV8662EVM demo board requires a 1 amp power supply. According to a posting online, the Arduino Nano can supply a Maximum current from 3.3v is 200ma and 5v is 1A. So I think that it's not the Arduino.

    To double check, I attached a fairly large cell phone battery that was 1200mAh and 3.7v. It was fully charged, so its output voltage was 4.15v. I attached it got the same results.

    So basically, the power indicator light blinks. When it blinks, I sometimes get a glimpse of a sine wave on my scope.

    I press the mode button 1 time and the indicator light goes to solid green. No change on the scope, no sinewave. AC Voltage across the output pins is 0.19vAC. I push the button again. Top light blinks, middle light is solid, bottom light is off. Same results. I press the button again and again, cycling through all 8 modes until I get back to the single blinking green light. All produce same results. Just 0.19vAC on output pins.

    So, I'm guessing this particular eval board is defective. Any way TI will send me a free replacement? The board cost $99. I got it free from a parts rep. I guess I could ask them for another one. Any other suggestions?

    Thanks,
    Curtis
  • 0 in reply to Curtis Harrison
    Intellectual 260 points
    This morning, I made a bench power supply from an old computer power supply. It provides 18amps at 3.3v and 12 amps at 5v. So I tried both the 3.3v and the 5.5v and got the same reaction from the DRV8662EVM.

    Here's the pattern I'm seeing.

    When power is initially supplied, the Active LED blinks 3 short blinks, then 1 long blink, then turns off and repeats the cycle.
    When it is doing the long blink, I can see a nice sine wave flash on my Scope.

    Similar behavior happens with every other push of the Mode change button. When the light is solid, I get flat line. When it is blinking, I sometimes get a flash of a sine wave.

    Yup, pretty sure this board is defective.. Any ideas on how to fix it would be great.. I resoldered all the pins on the bottom of the board, but I'm guessing it might need a trip through the surface mount machine.

    Thanks for your help so far. Any assistence with ways of bringing this board back to life would be helpful.
  • 0 in reply to Curtis Harrison
    TI__Expert 3791 points
    Curtis,

    Yeah, given that you tested it using a power supply and it still gave you trouble leads me to believe that there must be something wrong with the evaluation board.

    I would recommend reaching out to the part rep to see if they can provide you a working board. If not we can see what we can do from our side.

    Best Regards,
    Javier Palomo
  • 0 in reply to JP
    Intellectual 260 points
    I measured the capacitance of the piezo and it measures 3600 pF. Can the Drv8662 handle a load of that size? The datasheet doesn't seem to think so.
  • 0 in reply to Curtis Harrison
    TI__Expert 3791 points

    Hello Curtis,

    The DRV8662 is able to drive a 3600pF piezo, since there is not minimum capacitance on the output of the amplifier.

    Were you able to obtain a new board or are you still troubleshooting the original EVM?

    Best Regards,

    Javier Palomo

  • 0 in reply to JP
    Intellectual 260 points

    The rep we got it from doesn't work there anymore so we're trying to find another rep.  Do you know of any?

    I was worried about overloading it requiring 56vpp  at such high frequency of 25 kilohertz and thought the capacitance was too high. Seems like when we try to use voltage boosters and op amps as soon as we hook up the piezo  the voltage drops because it can't handle it. Just hoping this driver can handle it and it sounds like it will if we can get the driver to work at all. Do you know of a way we can get an eval board?