This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TAS2770EVM-STEREO: TAS2770 EVM to drive a voice coil actuator

Part Number: TAS2770EVM-STEREO
Other Parts Discussed in Thread: TAS2770

Hi, 

I am interested in using the TAS2770 EVM to test a voice coil actuator, in which I will need to send DC voltages/non-audio waveforms to my actuator from the TAS2770 output. Would I be able to do this with the EVM? Would I need to use PPC3, and would PPC3 support this? Is there an API of sorts to interface with the board via USB?

Also, a general question about I2S: can I drive two TAS2770s over a single I2S port (is this how stereo works)? Sorry, I am new to audio and using I2s in applications.

Thanks,

Chris

  • Hello Chris,

    Welcome to E2E. Thank you for your interest in TAS2770.

    Regarding to your questions about DC output voltage, the output of TAS2770 Class-D amplifier is a PWM waveform designed for 20 to 20 kHz response. In other words, the output will be constantly switching between -VBST, 0V, and VBST. The only way to get close to DC output is to use max duty cycle, but that won't allow you to adjust the output voltage unless you change the internal boost. You can test this out in PPC3>Device Control>Playback> Amplifier Level

    If you would like to use the EVM, you will need PPC3 and the PPC3 device plug-in to initialize and configure the EVM. 

    To your last question, Yes you can drive two TAS2770. We have TAS2770-Stereo model that specifically deigned for stereo application. In fact, you can connect multiple TAS2770 up to 8 channels. 

    Let me know if you have any questions. I will get back to you as soon as I can find a solution to your actuator needs.

    Regards,

    Jin Gao

  • Thanks so much for the answers Jin. So there isn't a way to interface with the EVM other than with PPC3 (i.e. no API available)? Could I generate custom waveforms and send to PPC3 to send to the EVM + actuator? 

  • Hello Chris,

    There is a way by directly initialize with I2C commands via external I2C communication. However, to get started with EVM, we usually recommend to use PPC3 to configure and initialize the device. PPC3 has a very user friendly UI and easy to use. 

    To your second question, yes you can generate custom waveform. PPC3 is only used to initialize the device and configure registers or specific device features. Once it is initialized, it can play any audio content using any audio player on PC. In your case, I would recommend o scope the output before testing it with the actuator, and like I said before about Class D audio amplifiers, I am not sure if it will fulfill your needs. 

    Regards,

    Jin Gao

  • Hi Jin,

    Thanks, this was helpful/resolved my questions!

    Best,

    Chris

  • Hello Chris,

    Sorry of the delayed response. I hope you are making good progress using TAS2770. After testing TAS2770 in the lab by one of our application engineer, we were able to verify that TAS2770 can actually output to any DC voltage by inputting a DC waveform and adjust the amplifier gain(either through volume control or amplifier gain). Both are located in PPC3>Device Control>Playback> Amplifier level and Volume.

    NOTE: In order to output DC voltage, make sure you disable the HPF. You can disable it by writing 0x00 to register 0x04. You can do that by either writing an I2C command or simply toggle the bits in PPC3>register map

    May I ask what output voltage are you trying to achieve? I believe some of the our haptic devices can also achieve similar results. 

    Please test it out and let us know if you have any questions. 

    Best regards,

    Jin Gao

  • Hi Jin,

    I'd like to follow up on this. What is the expected output from the coils supposed to look like? For some reason on my EVM, controlled via PPC3 and set as the default audio playback device, I am always measuring what appears to be some sort of frequency modulated signal composed of pulses, always at 12Vpp, regardless of my volume control and amplifier level settings. 

    I have no jumpers on J2 and J6, and a jumper on J12. Controlling over USB. I'd like to be able to get a constant DC voltage at a desired level. Could you please recommend how to do this? 

    Thanks,

    Chris

  • Hello Chris,

    May I ask what is the input signal that is feeding into the EVM, and what output voltage range are you trying to achieve? 

    Regards,

    Jin Gao

  • Hi Jin,

    I have tried both playing audio over USB from my computer with PPC3, as well as sending a constant binary value over I2S from an STM32 microcontroller, making sure to adjust the jumper wires according to the EVM user manual for USB vs external input. In both cases, I am seeing 12Vpp pulses that vary in width and frequency at the output, rather than a continuous waveform at different amplitudes. 

    I'm hoping to be able to set any voltage output between 0-12V. 

    In theory, could I just send a binary value over I2S and have it produce a constant signal? 

    "After testing TAS2770 in the lab by one of our application engineer, we were able to verify that TAS2770 can actually output to any DC voltage by inputting a DC waveform and adjust the amplifier gain(either through volume control or amplifier gain). Both are located in PPC3>Device Control>Playback> Amplifier level and Volume." 

    Would it be possible for me to see the register settings for this setup?

    Thanks so much,

    Chris

  • Hello Chris,

    Yes. I can send you the PPC3 Setting. Give me some time to verify it and upload it. I believe the test done in the lab was measured after the filter. The frequency modulated switching is normal. It is the PWM switching even if the input is a constant value. As long as you have disabled the HPF in the register, you should able to adjust the amplifier level or volume and see the DC output after you add the low pass filter (<20 kHz or even lower depend on your application) to filter out the PWM. 

    Regards,

    Jin Gao

  • Hi Jin,

    The lowpass filter you are referring to is a additional external circuit, not in the TAS2770 or EVM, correct? I.e. the ferrite bead in the application circuit.

    Thanks, take your time with the register settings - I appreciate it!

    Chris

  • Hello Chris,

    You are correct, the low pass filter is indeed an additional external circuit. The ferrite bead filter refereed in the datasheet is mainly for output EMI concerns, but any low pass with appropriate cut off frequency should work.

    Regard,

    Jin Gao