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TPA3255: Protecting analog inputs

eugenio
Expert 1505 points
Part Number: TPA3255

Hi all!

In TPA3255 datasheet, it's stated that any voltage over 7V and below 0.3V on any analog input could cause permanent damage:

Should I include a precise peak limiter before the two phase-reversing opamp? (red box on EVM schematic):

I mean precise because a simple diode clipping can not both protect from overvoltage and avoid distortion at levels close to full power, because of the non ideal voltage knee near turn-on.

What happens if, in TPA3255EVM, someone applies a voltage exceeding 3.5Vpk (say 3.55Vpk, or 2.51Vrms 1kHz sinewave) on any RCA audio input? 

  • 0
    TI__Mastermind 19080 points

    Hi,

    Yes, it could be at the position you proposed, or directly on the "INx" nodes on the EVM.

    As said on datasheet, "Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

    only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
    Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability."

    Hopefully this description could help you to understand the maximum limitations. Thanks!

    Regards,

    Sam 

  • 0 in reply to Sam(MPAA) Zhang
    Expert 1505 points

    Thank you for your reply.

    I've come up with a simple limiter circuit at an expense of a couple of opamps, but there is still something not clear to me.

    I've measured the biasing voltage at INPUT_x pin (with no signal applied), and it's close to 3.8V. This is exactly AVDD/2:

    In the same datasheet, few pages later, there is this design example:

    INPUT_x voltage should be +-3.9V peak max. This voltage, summed up with +3.8V of input bias, will exceed the +7V absolute maximum limit (albeit close to AVDD, so no body diode turn on will occur in normal conditions).

    Is this a typo, or the absolute maximum rating is somewhat over conservative?

  • 0 in reply to eugenio
    TI__Mastermind 19080 points

    Hi,

    Please follow the information in EC table... Voltage on the INPUT_X to GND should not exceed the range of 0~ 7V, which means the limit on the input should be ~+/-3.5Vpeak.

    Thanks!

    Regards,

    Sam