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LM4946: 4ohm load possible with LM4946 without lower power

Mete Yasan
Intellectual 500 points
Part Number: LM4946
Other Parts Discussed in Thread: LM4947

Hi,

The customer is going with LM4946 on their design. However, their loadswitched to 4 ohm from 8  ohm because of a special reason. 

We know LM4946 matchs with 8 ohm load.

Is there a way to use LM4946 with 4 ohm load without decreasing power?

Thanks,

Mete

  • 0
    TI__Guru** 102045 points
    Hi Mete,

    Using a lower load will increase current consumption and thus power dissipation. You must lower the output level to avoid an overcurrent or damaging the device.
    You should test performance with lower impedance load, however data sheet specs and data is not guaranteed as this use case is out of spec.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Intellectual 500 points
    Hi Ivan,
    Thanks for your response.
    The customer will try with 4ohm. they will decrease the gain but output current will still increase.
    The point is, when the output voltage is decreased by gain, peak currents for PWM will (may) be high (only average current will be decreased)
    There is no sufficient information for detailed information about architecture of the device. Is there an internal filter at the output? Is it about "Boomer" architecture?
    In the datasheet there is a OCL (output capacitor-less) subject however it seems that it is not related to speaker output.
    How can we find more details about the output architecture of LM4946?
    Thanks and regards,
    Mete
  • 0 in reply to Mete Yasan
    Intellectual 500 points
    Hi all,
    Can you please help on this case?
    Thanks,
    Mete
  • 0 in reply to Mete Yasan
    TI__Guru** 102045 points
    Mete,

    The OCL refers only to the headphone outputs, Rout and Lout. In OCL mode the Voc pin generates a center voltage reference for the single-ended output loads, this allows to eliminate the AC coupling capacitors at the output.
    LM4946 mono (speaker) output should not be a PWM, it doesn't mention Class-D architecture.
    LM4947 in the other hand is a Class-D variation of the same device.

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