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LM4865 Enquiry

Philip
Expert 1510 points
Other Parts Discussed in Thread: LM4865, LM4838, LM4836, TPA0253, TPA0211

Hi,

Would like to get your advice on LM4865M application.

Intend to change the speaker load impedance from 8ohm to 4ohm.

Could you please advise whether it is OK to use this part based on below conditions?

DC Supply: 3.4 to 4.2V

Speaker Load: 4ohm

Speaker Power Rating: 1W (max 1.5W)

Target is to achieve 500mW at THD=1% (Bridge Mode).

Package: SOIC.

Normal ambient temperature: 25 Degree (with operating temperature is -15 to 60 deg).

Note: Based on calculation ,power dissipation seems OK.

But under LM4865 spec/performance characteristic, it does not mention this device can support 4ohm load impedance.

Is there any potential issue for this device to support the design application?

Thanks,

Phil

  • 0
    TI__Mastermind 20085 points
    Hi Philip

    The device won't be able to work with RL=4Ω because the power dissipation will be higher than maximum power dissipation and the device could be damaged for this condition.
    Please let me know your opinion or if you have more questions.

    Best regards
    José Luis Figueroa
    Audio Applications Engineer | A-Team
  • 0 in reply to José Luis
    Expert 1510 points
    Hi Jose,

    Thanks for your reply, understand your explanation based on calculation.
    I have another question.
    Does TI have any same series part for this LM4865 Class AB power amp (with mono speakers channel) which can support 4ohm load or higher output power?
    Note: Special features such as DC Voltage Volume control, Headphone Amplifier Mode are still needed.

    Best Regards,
    Philip
  • 0 in reply to Philip
    TI__Mastermind 20085 points
    Hi Philip

    You could take a look to the following devices LM4836 and LM4838, they are Stereo Audio Power Amplifier, but they have other features.
    Another device that you could use it's the TPA0253, but It doesn't have DC Voltage Volume control.
    Please let me know your opinion.

    Best regards
    José Luis Figueroa
    Audio Applications Engineer | A-Team
  • 0 in reply to José Luis
    Expert 1510 points

    Hi Jose,

    I am looking at TPA0211.

    And based on TPA0211 spec (below settings conditions)/under THD=1%, can you advise what is the maximum output power (Vdd=3V, Rload=4ohm, BTL mode spec does not have info on this)? How about the max output power for THD more than 10%?

    Please do kindly advise.

    Thanks,

    Philip

  • 0 in reply to Philip
    Expert 1510 points
    Hi Jose,

    Additional info:
    Typical of maximum power output is 660mW under Vdd=3V, Rload=4ohm, BTL mode, Ta=25degC (refer Page 4 spec).
    Please advise the maximum output power under THD=1% and THD=more than 10%.

    Thanks.
  • 0 in reply to Philip
    TI__Mastermind 20085 points

    Hi Philip

    Sorry for the delay. Unfortunately, I don't have an EVM to obtain this information, but you could refer the figure 12 of the amplifier's datasheet to find more information. 

    Best regards
    José Luis Figueroa
    Audio Applications Engineer | A-Team

  • 0 in reply to José Luis
    Expert 1510 points

    Hi Jose,

    I checked Figure 12 but this figure only refers to typical characteristic of THD+N vs output power.

    Do you have any information on maximum output power spec as this is info is missing from the spec (refer Page 3 spec, only have typical info)?

    Refer as per below for the highlighted red box, please kindly advise.

    Best Regards,

    Philip

    2016-03-04_102140.pdf

  • 0 in reply to Philip
    TI__Mastermind 20085 points
    Hi Philip

    I don't have an exact value, but it shouldn't change much regarding typical value. Regarding figure 12 when the device reaches a THD+N=10%, it almost gets 1 W.
    Please let me know your opinion.

    Best regards
    José Luis Figueroa
    Audio Applications Engineer | A-Team