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LME49811 internal diagrams?

Hi forum,

I wonder whether I could find the internal diagram for this device?  (the "equivalent schematic" or "simplified schematic" that usually shows in the datasheets).  I'm mostly interested in the 49811, but same info for the 49810 and 49830 would also be great.  Also, if it is a simplified schematic, hopefully not too simplified.

The reason I ask is:  one problem I see with these LME is the lack of protection circuitry --- I would like to try adding that, but I'm not sure what's driving pins 13 and 14 (source and sink), so I don't know whether I can connect a collector that pulls that signal towards GND when output current exceeds the threshold.

Any advice on this subject will be appreciated.

Regards,
Carlos
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  • Hi, Carlos,

    Unfortunately, we don't have a block diagram other than the one in the data sheet. We have not tried adding external protection, hopefully someone in the forum has experience doing this.

    -d2

  • Thank you Don!

    Follow-up comment:  there is no block diagram in the LM49811 data sheet!  There are simplified block diagrams for the 49810 and the 49830, so assuming the 49811 follows the same idea, it looks like source and sink are the emitter of output transistors --- I don't think I can connect the collector of an external transistor hoping to pull that signal towards GND, right?

    So, let me try the following:  do you think the following circuit  (attached image below --- notice the two added resistors) will work without considerable capacity or quality degradation?

    Thanks,
    Carlos
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  • Hi, Carlos,

    Unfortunately, I am not familiar enough with this device to give you any advice.

    Maybe someone else in the Community may have advice for you.

    -d2

  • Thank you Don,

    Yeah, maybe someone else who has tried or thought about this might jump in!

    I can always try --- the circuit is not extra-complex, and the chips are not extra-expensive, so maybe I'll end up just trying and measuring!

    Best regards,
    Carlos
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  • Hello Carlos-san,

    I attached very much simplified schematic of LME49811 and an idea of current limit on output Trs as below.

    3527.Simplified schematic & an idea of current limit.xlsx

    I hope this information will be helpfull for your design.

    Best regards

    T NAOKAWA

  • Toyojiro,

    If I understood correctly your diagram, this is very similar to the idea I have in mind --- but the question remains:  can we connect those transistors (the collectors) to the source and sink pins of LME49811?  It looks like those pins are driven by the emitter of a "follower" transistor  (extrapolating from the block diagrams of the 49810 and 49830), so I'm not sure that this connection would be valid.

    So, I will ask you:  have you tried the configuration that you show in the schematic that you posted?  did it work?

    My follow-up question was related precisely to this --- if there was a high-enough resistor between the 49811 pins and the base of the Darlington transistors, then I could connect a collector that pulls the signal towards GND.  But then, would those resistors  (10k in the example I posted) disrupt the functionality of the circuit?  Hmm, maybe if I placed them after the Qmult transistor?  (i.e., so that the Qmult transistor and the two resistors remained connected directly to the source and sink pins, and then the 10k resistors were between those and the base of the Darlington transistors?)

    Regards,
    Carlos
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  • Hello Carlos-san,

    LME49811 is just one channel version of LM4702 which is stereo channel version with 5.5mA source/sink output current. LME49811 increased output current slightly to 8mA or 9mA depend on applied voltage. And LME49810 has emitter folloowe to increase output driving capability and LME49830 has also emitter follower to drive gate capacitance of output MOS FET. But LME459811 has no emitter foloower. Unfortunately I don't have LME49811 sample but I had LM4702 sample and checked current limit idea with LM4702 and confirmed it worked well. I am requesting LME49811 sample and as soonas I received, I'll check the idea. It should be worked.

    When you put high value resistor like 10k between LME49811 pins and the base of darlington Trs and put current limit transistor like I posted, it will also work but the voltage on the source pin for example, it will reach top side saturation and sink pin will be as well because current limit sense Tr will sink output current of LME49811. If the device operates under +/- 50V for example, the voltage across the 10k resistor will be 8mA x 10k=80V but this will saturate source pin at supply voltage.  So I don't think it is good idea to put high value resistor.

    If you want, I'll response the result of current limit idea I posted after I received LME49811 sample.

    Best regards

    T NAOKAWA

  • Thank you again, Toyojiro,

    I think I understand now --- in your earlier post, I overlooked one detail in your diagrams, so I wasn't sure.  But good to hear that this configuration you posted works!  That certainly makes it simpler to implement, and I think it should not introduce much distorsion  (if at all!)

    I will definitely try it --- but if you want to let us know of any results you got, I will be more than happy to hear about it!

    Best regards,
    Carlos
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  • Hello Carlos-san,

    I just got LME49811 sample and checked current limit idea which I posted earlier and confirmed it worked well. To get symmetrical current limit value, you will tune or select the current sense Tr characteristics for both NPN and PNP.Then you will get symmetrical value.

    Best regards

    T NAOKAWA 

  • Thank you Toyojiro!

    Good to hear that the technique works with the LME49811 --- in the mean time, I have been doing some simulations through circuitlab, just using an op-amp followed by a push-pull output pair with two diodes to reduce crossover distortion.  Seemed to work quite well;  so next I'll try it with the LME49811.

    Again, thanks for your comments and ideas!

    Best regards,
    Carlos
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  • hi,

    the lme49811tb can be designed as an audio power amp with current limit,you must use the Shutdon pin wit a few  transistors to do that...

  • ohh how can we use the current limiting option? please suggest me i have already blown my speaker with this issue..

  • dear LMe49811tb user,

    you must use an small signal PNP transistor to sense the current in the emitter resistor and use the collector to turn on an NPN transistor that is used to pull down the shutdown pin via a resistor...