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Thread: Teensy Audio Shield LINEIN Input Level Limit

  1. #1
    Junior Member
    Join Date
    Jul 2021
    Posts
    3

    Teensy Audio Shield LINEIN Input Level Limit

    Hello, I have to feed a 16Vpp signal into Teensy audio shield. I read SGTL5000 has max 2.83Vpp limit for LINEIN. I have some questions
    1. What happens if input exceeds the 2.83Vpp limit? Would the reading just saturate or SGTL5000 will be damaged?
    2. What would be the best option to scale the input signal down to fit it into the acceptable range?

    Thanks

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    1,250
    Like all CMOS chips a pair of Schottky diodes to the rails and a series resistor will do the job of protecting inputs.
    To my knowledge exceeding the rails in the inputs by more than a diode drop risks damaging the chip, just like
    other CMOS chips.

    You can add a second resistor to ground to form a potential divider with the series resistor to attenuate the input.
    With enough attenuation the diodes aren't needed. The values of the resistors depends on the source impedance,
    but you could try 10k : 2k2 divider (16Vpp becomes 2.9Vpp)

    This isn't ideal from a noise perspective, lower resistances are better, but if the load can't drive a low impedance
    that would preclude something of lower resistance.

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