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LM48511: Gain setting question for 4ohm/5W output

Part Number: LM48511
Other Parts Discussed in Thread: TAS2521, TAS2552, TPA3110D2

Hi Sir,

We have a project using LM48511 for a 4ohm/5W output application and the input signal is around 233mVrms.

So in order to achieve 5W output we set the Gain setting as 2 X Rf(39K) /Rin(10K) = 7.8. And with that setting, the LM48511 on customer's board will be damaged.

We also verify it on EVM with above setting, the LM48511 on EVM will also be damaged. EVM Setting as below.

R5=20K, R7=20K , R6=30k, R8=30k, R3=22k ->VDD=5V, Boosted Vout = 7.3V, VFB=1.32V , FB_SEL=High

We also try below conditions:

1. input:1.2Vrms, Gain:3.9, output 5W, LM48511 works.

2. input:1Vrms, Gain:4.7, output 5W, LM48511 works.

3. input: 880mVrms, Gain 5.6, output 5W, LM48511 will damaged.

4. input 230mVrms, Gain 7.8, LM48511 will damaged.

Here is my question:

1. Could we set the Gain of LM48511 higher than 5.6?

2. If we would like to have a 5W output with 4 ohm speaker, what is the maximum gain and minimum input signal that we should set?

This is a urgent case, because customer change to our solution before last build and they are going to build final build tomorrow, we need your help to provide a suggestion.

Many thanks,

Patrick

  • Hi Patrick,

    1 and 2) You should take into account the device output to set gain and input signal, it means that the input signal and the gain shouldn't produce the clipped output signal as this causes higher distortion and increases power consumption.
    I recommend you to review the output signal in all the cases to avoid to get clipping. I think that the output signal is clipped in all the cases where the device is damaged.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • Hi Joe,

    Thanks for helping, we will verify the waveform and update it.
    Before we got the waveform, let me list down my test result more detail.
    We are using AP to run the test.

    1. input:1.2Vrms, Gain:3.9, output 5W,THD+N 2.5%, LM48511 works.
    R5=20K, R7=20K , R6=39k, R8=39k, R3=24k ->VDD=5V, Boosted Vout = 7.9V, VFB=1.30V , FB_SEL=High

    2. input:1Vrms, Gain:4.7, output 5W, THD+N 3.1%, LM48511 works.
    R5=20K, R7=20K , R6=47k, R8=47k, R3=24k ->VDD=5V, Boosted Vout = 7.9V, VFB=1.30V , FB_SEL=High

    3. input: 880mVrms, Gain 5.6, output 5W, THD+N 15.1%, LM48511 will damaged.
    R5=20K, R7=20K , R6=56k, R8=56k, R3=24k ->VDD=5V, Boosted Vout = 7.9V, VFB=1.30V , FB_SEL=High

    4. input: 500mVrms, Gain 5.6, output 2W, LM48511 will damaged.
    R5=20K, R7=20K , R6=56k, R8=56k, R3=24k ->VDD=5V, Boosted Vout = 7.9V, VFB=1.30V , FB_SEL=High

    5. input 230mVrms, Gain 7.8, LM48511 will damaged.
    R5=10K, R7=10K , R6=39k, R8=39k, R3=24k ->VDD=5V, Boosted Vout = 7.9V, VFB=1.30V , FB_SEL=High

    1. And as you could see on test case 3, THD+N is 15%, Do you think this is big enough to damage the LM48511?
    I think we still need your help to advise below question, I think we should be able to know our IC ability with a specified output case, could you help?
    2. If we would like to have a 5W output with 4 ohm speaker, what is the maximum gain and minimum input signal that we should set?


    Thanks,
    Patrick
  • Hi Patrick,

    is the thermal pad properly soldered to the ground plane?

    Kai
  • Hi Patric,

    1,2) This device is very old and doesn't exit a lot of information. It seems that the package is very tiny to handle this power. The dissipation would be very high and the IC would get too hot. I think the power of 5.4 W has been measured with a burst signal from the Audio Precision(AP). I have supported other customers with this problem, but It seems that this device is not able to achieve this output power without having problems.
    Below you can find some refers:
    e2e.ti.com/.../622609
    e2e.ti.com/.../296571

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • Hi Jose,

    Got it, thanks for your answering, we will suggest customer to change solution.

    If LM48511 could not support 4ohm/5W with this tiny package, Should we modify the spec to prevent other customer use it on a 5W application?

    Or you could come out any reference design to show us how to implement it with 5W application? Like layout guide, Gain setting, components selection.

    Patrick

  • Hi Patrick,

    You are correct. The specifications of the datasheet should be modified.
    As this is an old device and the information is reduced, so I haven't seen any reference design about this or something like that before.
    They could have a look at the following devices: TAS2552 and TAS2521. They could fit in your application.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • Hi Jose,

    We are thinking to promote TPA3110D2 to customer due to we have this EVM on hand right now.
    we also found that TPS3111 should also work, but we currently did not have EVM to test, so we will promote the TPA3110D2 first.
    Do you think this also ok for 8W/4ohm application?

    Thanks,
    Patrick
  • Hi Patrick,

    This device fits in this application. In fact, the device can deliver an output power much higher without problems.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer