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TAS2770: Audio performance degradation due to VBAT fluctuation

Tamio Yokokura
Expert 3630 points
Part Number: TAS2770

TAS2770 support team

TAS2770 supports battery voltage range between 4.5V and 16V as the datasheet mentioned. But the datasheet is not mentioned the audio performance when VBAT is dynamically variated. According to my estimation, the voltage fluctuation is approximately 1.7V at typical case. When VBAT variates 1.7V with 2.5A/us of slew rate due to the system heavy load, will the audio performance degrade? If YES, can you show the degradation quantitatively? And also, does the noise issue?

Regards,

Tamio

  • 0
    TI__Guru* 84915 points
    Hi, Tamio,

    When the TAS2770 is powered up, it is always important to have all the power supplies completely stable before its usage. As suggested in the Power Supply Recommendations, VBAT is the first power supply that must be stable, even before IOVDD and AVDD. Please remember that VBAT is the power supply for the Class-D driver, any variation on the supply will also affect the Class-D driver output.

    The degradation in this case cannot be described in a single number since VBAT affects many parameters of the device. Some important parameters involved are:

    - THD+N.
    - Idle Channel Noise.
    - Output Power.
    - Efficiency.
    - PSRR (db).

    (For all the parameters above, please take a look at 6.9 Typical Characteristics section of datasheet for details).

    - VPK or maximum peak unclipped output voltage ( www.ti.com/.../tas2770.pdf )

    Due to the different parameters affected, it is not possible to explain the degradation in a single number. Instead of that, I recommend to check how each parameter can be affected dynamically. In addition, we don't recommend to have a high ripple in the VBAT voltage since it must be stable as recommended in the Power Supply Recommendations section of datasheet.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    TI__Expert 3630 points

    Hi, Luis

    Thank you for your reply.

    As far as I see your comments, I understood that VBAT can support a wide range as the input voltage, but it must be stable, not variable when TAS2770 is operated. Therefore, VBAT is not recommended to connect directly to the battery pack in system because the voltage of battery pack variate due to the system load current. And also, your recommendation is that DCDC converter uses between battery pack and VBAT of TAS2770.

    Is my understanding correct?

    Thanks

    Tamio

  • 0 in reply to Tamio Yokokura
    TI__Guru* 84915 points
    Hi, Tamio,

    Your understanding is correct. Thank you for provide your summary about VBAT.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    TI__Expert 3630 points
    Hi, Luis
    Since customer misunderstand that VBAT can be connected directly to battery which voltage varies with a system load, I hope that PIN name of VBAT is changed to other name so that customer don't misunderstand. And also, I would like you to add the description that VBAT must apply the stable voltage in datasheet.
    Thanks
    Tamio