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DRV8662: I can not get the device to give me any output signal

Gabriel Winterstein
Prodigy 50 points
Part Number: DRV8662

Hello,

I would like to use the DRV8662 Piezo Haptic Driver in my bachelor thesis and I need help with the  output. I have the DRV8662 chip itself and the DRV8662EVM evaluation board. With the chip I build my own evaluation board with the same schematic around the chip than the DRV8662EVM except for the input. On both boards I am using a simple low pass filter on IN+ and IN- is connected to GND over a 100nf capacitor. The cut-off frequency is around 2600Hz. All the gain pins on both boards are LOW.

If I connect a waveform generator with a simple sine wave to both the boards the DRV8662EVM gives me an output signal but my own board does not.
I am guessing that there is something wrong with the input but I can't discover what it is because the external components are exactly the same on both boards.

If I measure the differential input on both boards I gets this result on the scope:

CH1 is the input signal directly measured at the waveform generator. this signal goes to the low pass filters of both the boards. (later on I am planing on using a PWM signal)
CH5 (red) is the input measured directly at the input pins form the DRV8662 of the  DRV8662EVM.
CH3 (purple) is the input measured directly at the input pins form the DRV8662 of my board.

Even If I disconnect the power but keep the sine signal turned on at both boards I get different signals at the two boards which are shown in the next picture:

labels are the same.

But it can't be the low pass filter, because if I disconnect both DRV8662 chips from the low pass filter I get this result

CH3 and CH5 are the identical. 

Is the chip on the DRV8662EVM not the DRV8662? Or is there something broken on my board?

Does anyone know what could be wrong?

Kind Regards

Gabriel Winterstein

  • 0
    TI__Intellectual 1910 points

    Hey Gabriel,

    Is the EN pin high? When the EN pin transitions from low to high, the amplifier turns on. 

    If that is not the issue, then it would be helpful to see your schematic to verify the necessary components. 

  • 0 in reply to Micah B Brouwer
    Prodigy 50 points

    Hi,

    sorry for the late reply. Email accidently went into the SPAM folder.

    The EN pin is high and I also get boost voltage and vpump.

    The schematic ist the same then the one for the evaluation board.

    Except EN goes to VBAT and Gain0 and Gain1 to GND.

    On In+ and In- I am using a different input filter. 

  • 0 in reply to Gabriel Winterstein
    TI__Intellectual 1910 points
    To verify the board is working, try bypassing the low pass filter at the input for now and see if you get an output.

    Also, what is your boost voltage?
  • 0 in reply to Micah B Brouwer
    Prodigy 50 points

    Bypassing the low pass does not help with the output. Even if I connect a sine wavegenerator.

    Boost voltage is around 30V.

    How sensitive is the chip concerning the layout?

    My circuit is put together with THT components and the DRV8662 is connected with a SMD to THT adapter board.

  • 0 in reply to Gabriel Winterstein
    TI__Intellectual 1910 points

    There are some layout guidelines listed in the datasheet:

    11.1 Layout Guidelines

    • To achieve optimum device performance, use of the thermal footprint outlined by this datasheet is recommended. See land pattern diagram for exact dimensions. The DRV8662 power pad must be soldered directly to the thermal pad on the printed circuit board. The printed circuit board thermal pad should be connected to the ground net with thermal vias to any existing backside/internal copper ground planes. Connection to a ground plane on the top layer near the corners of the device is also recommended.

    • Another key layout consideration is to keep the boost programming resistors (R1 and R2) as close as possible to the FB pin of the DRV8662. Care should be taken to avoid getting the FB trace near the SW trace.

    It is strange that the chip is behaving in this manner. Even with an analog input, it is important to have the AC coupling capacitors in place (0.1 uF) at the input. It may be helpful to ensure that none of the pins are shorted together by probing for continuity. If all else fails, it is possible that the chip was damaged and is not operating correctly, and I would recommend trying again with a new chip. 

  • 0 in reply to Micah B Brouwer
    Prodigy 50 points

    I saw the layout example in the datasheet but do you think that it is possible that there is no meaningful output at all with a diffenrent layout?

    AC coupling capacitors were always in place at the input..

  • 0 in reply to Gabriel Winterstein
    TI__Intellectual 1910 points
    With just minor alterations to the input filter, the ouput will be different, but there should still be an output. Did you ensure that no pins were shorted?
  • 0 in reply to Micah B Brouwer
    TI__Intellectual 1910 points

    Hey Gabriel,

    Any update on this? Did you try using a new IC?

  • 0 in reply to Micah B Brouwer
    Prodigy 50 points
    Hi,

    yes I also tried a new IC. It seems like the boost voltage causes problems. If I connect an external 30V to PVDD instead of the VBST there is an ouput but still far away from the output of the evaluation board. I implemented this chip into my layout hoping that the layout is the reason for the unexpected behavior of the output. If that still doesn't work I can throw away my circuit board and start again with a different chip.

    Regards,

    Gabriel Winterstein