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Original question:

LM48511: LM48511 supports single input

LM48511: Can it accept PWM inputs instead of "pure analog sine wave" from a microcontroller ?

Jerry Zeng
Prodigy 70 points
Part Number: LM48511


Since many microcontroller has PWM outputs, if LM49511 can support PWM inputs, then then design will be much more efficient. 

  • 0
    TI__Guru** 110745 points
    Hi Jerry,

    You can use a PWM as input signal, however you must place a Low-Pass Filter between PWM output and LM48511 input.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Prodigy 70 points

    Hi Ivan:

    I notice that LM48511's inputs are all AC coupled, in this case, if I feed in two PWM signals to them, should they be ok?

  • 0 in reply to Ivan Salazar
    Prodigy 70 points
    And by the way, Ivan, which ground should the thermal pad connect to ? In the datasheet of the chip, it suggests that this thermal pad should be connected to the signal ground, i.e, GND2, but in the demo board user guide (AN-1922), the thermal pad seems to be connected with GND3, which is the ground of boost converter. which senario should I follow? Thanks, Jerry
  • 0 in reply to Jerry Zeng
    TI__Guru** 110745 points
    Jerry,

    If input signal is a PWM it still needs low-pass filter. AC couple would remove the DC bias, however it will most likely continue being a square-wave signal.
    Regarding the thermal pad, you should solder this to GND plane for dissipation purposes. In the case of the EVM it is not connected on the top layer to any of the GND pins, layer 1 is used for GND2, layer 2 is used for GND1 while bottom layer is used to connect all GND1, 2 and 3, as well as thermal pad.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Prodigy 70 points

    Thanks for your answer, Ivan.

    I'm just wondering, will the sigma-delta control loop of the class D amp filter out these high frequency stuff in PWM? I didn't find any information about the bandwidth of the loop in the datasheet.

    If you can provide several insights on this subject, it will be awesome!

    Thanks, Jerry

  • 0 in reply to Ivan Salazar
    Prodigy 70 points
    In the application document, it uses 4-layer PCB configuration, is 2-layer configuration acceptable?
  • 0 in reply to Jerry Zeng
    TI__Guru** 110745 points
    Jerry,

    2 layer board would be OK.
    This is an analog input device and it is not meant to be used with PWM-like signals. As mentioned before, if this is needed an external low-pass filter must be placed at the inputs. Unfortunately there is not much more information available that can be shared of the internals of the device.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators