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TLV9144: Receives external noise.

Ryu Yamashita
Genius 3705 points
Part Number: TLV9144
Other Parts Discussed in Thread: OPA1678

Tool/software:

Hi team,

We were interested in this device because of its low power consumption, and when we replaced it with a device from another company, it picked up a lot of external noise.
I am using it for audio signals, but the noise is on the audio output.
Is there any recommended countermeasure?

Best Regards,
Ryu.

  • 0
    TI__Guru* 77401 points

    Hi Ryu, 

    The TLV9144 is really designed for audio application. 

    One of low cost audio IC is OPA1678, which is designed for audio application. TLV9144 is not suitable for audio application, it does not slew rate, BW, THD+N ratio,  high open loop output impedance etc... Yes, it is designed for low power application, but for audio. If you measure the output signal in TLV9144, the audio output signals may be distorted and it will not meet audio application requirements. 

    If you have other questions, please let me know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Genius 3705 points

    Hi Raymond,

    Thanks for the reply.
    Regarding the OPA1678, I have used it.
    I understand that the RLV9144 is not for audio, but I want to use this device because of its price and power consumption.
    I would like to counteract noise on the input, so if you have any good countermeasures, please let me know.

    Best Regards,
    Ryu.

  • 0 in reply to Ryu Yamashita
    TI__Guru* 77401 points

    Hi Ryu, 

    Ryu Yamashita said:
    I am using it for audio signals, but the noise is on the audio output.

    Please show me the driving schematic. What load are you driving? In addition to what I mentioned about limitation, the TLV9144's output current is limited. as well (Isc or short circuit current is +/-40mA, but actual driving current is significantly less).  What  kind of noise are you hearing from the headphone? 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Genius 3705 points

    Hi Raymond,

    I apologize, but it was not an audio signal.
    I use it to detect piezo waveforms.
    It is not audible as sound, but occurs as input noise to the ADC.
    The specific noise is as follows.
    Frequency: Approximately 36 kHz
    Amplitude: Approximately +/-25 mV

    It also appears to be affected by power supply noise originating from the MCU, and we are considering various countermeasures.
    Please let us know if you have any useful countermeasure methods.

    Best Regards,
    Ryu.

  • +1 in reply to Ryu Yamashita
    TI__Guru* 77401 points

    Hi Ryu, 

    Ryu Yamashita said:
    It also appears to be affected by power supply noise originating from the MCU, and we are considering various countermeasures.

    I see. Based on the PSRR plot in the datasheet, the TLV9144 has a reasonable PSRR at lower frequency. The part is meant to be used in battery powered device. 

    Here is what you can try. At the V+ supply rail (assume you are using single supply rail), please add 100ohm resistor + 16uF to 22uF capacitor to form a LPF filter. With 100ohm/22uF, it will have a cutoff frequency approx. 72Hz (use Tantalum capacitor or low ESR electrolytic capacitors). This will improve the PSRR rejection significantly and will not be significantly affected CMU. 

    In addition, in the CMU's power rail, use larger low ESR bypass capacitor, up to 10uF or 22uF and this will get rid of noise generated by MCU (say PWM or other square wave related noises. Pay attention to DC bias derating in capacitors, if small C package is used.).

    You may also consider to use ferrite bead next to the power rail of MCU, but you need to make sure that the voltage rail is properly dampened with capacitors to avoid Q effects. 

    If you have other questions, please let me know. 

    Best,

    Raymond