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LM3886: Stability when LM3886 gain is set below 10 (gain 10 is datasheet required)

yiting.wang
Prodigy 25 points
Part Number: LM3886
Other Parts Discussed in Thread: LM4766

Hi Ti 

Due to their special need. The customer need to design LM3886 at non-inverting gain at 4 or less. Also, The LM3886 needs to output 1A to drive an 8 ohm load

I read carefully the article about unity-gain stable amplifier compensation method from bruce  https://www.edn.com/op-amps-g1-stable-decompensated/   and post from collin   https://e2e.ti.com/blogs_/archives/b/thesignal/posts/taming-oscillations-the-capacitive-load-problem

I think these method are suitable for capacitive load ) , but for non-unity gain stable (decompensated )  such as LM3886, I didn't see much info  

I try non-inverting gain 4 with 1pF~5pF and it is stable and works in the reality (non-inverting gain 3, 1pF-5pF is OK in TINA but fails in the reality. Gain 4 and 5 has more phase margin)

May I ask other method (and some related post) for  non-unity gain stable (decompensated)  op-amp ? 

I aslo try RC in feedback, but phase margin is negative..

  • +1
    TI__Mastermind 37710 points

    Hi Yiting

       I'm really sorry that we may not able to help you directly with this device. There's very little information left for this device, and we don't have research results about this point. The datasheet indeed states unstable situation may meet when the Gain smaller than 10.

       May I ask do we need an audio amplifier right now? Because our team is mainly working on the Class-D audio amplifier, could we consider using more recently devices, like the analog input TPA3128, or digital input TAS5825.

  • 0 in reply to Shadow He
    Prodigy 25 points
    Shadow He said:
    the analog input TPA3128

    Hi He

    Thanks for your reply

    We are using the audio amplifier as a simple amplifier  circuit  to perform 10kHz, 1A to 8 ohm load. Because LM3886 has great THD+N

    Would you recommend some analog input /analog output audio amplifier that has good THD+N?

    Regards

    Yiting

  • 0 in reply to yiting.wang
    TI__Mastermind 37710 points

    Hi Yiting

       Sadly seems the Class-D amp doesn't have such low THD. Please check if TPA3138 could be used.

       And another Class-AB product, LM4766 also has good THD value, it's not our group's product. You could raise another Thread about this device if interested.