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I am using the LM4871 and have problems with EMC interfiering Signals make the amplifier osscillating

Rolf Binder
Prodigy 40 points
Other Parts Discussed in Thread: LM4871

I am using the LM4871 and have problems with EMC, interfering Signals make the amplifier oscillating (osscillating at 14MHz) and my device is responding to cellphone interference too.

It seem the amplifier is way to fast!?

Is there a better amplifier choice?

  • 0
    TI__Mastermind 20085 points

    Hi Rolf,

    Welcome to E2E, thank you for your interest in our products.
    Could you please provide me more details about your issue?
    Regarding another device, You could use a Class-D Audio Amplifier, It has higher efficiency than a Class AB Audio Amplifier, you could have a look in our product folder in ti.com.

    Best Regards
    Jose Luis Figueroa
    Audio Applications Engineer | A-Team

  • 0
    Prodigy 40 points
    Hi Jose,
    thank you for your email.
    I am using the LM4871 in a medical device, two times, for signaling tones and for speech output.
    The amplifier works but when I hold my dealing cellphone close or in the emc immunity test, the amplifier is creating loud noises.

    Please find attached the extracts from circuit diagram and 2 screen shots with the output while radiated with the cellphone.
    I also shielded the board, but was not successful.

    The emc person in the testlab recommended using a slower amplifier.
    What could you recommend to me?

    Thank you very much, for your help,
    Rolf Binder 
    Rolf Binder (GF)
ONDAMED GmbH
rolf-binder@ondamed.de
www.ondamed.de
D: +49 (0) 7824 6466-0
    Am 01.08.2016 um 21:50 schrieb Figueroa Jose Luis:

     

    A Message from the TI E2E™ Community

     

    Figueroa Jose Luis replied to I am using the LM4871 and have problems with EMC interfiering Signals make the amplifier osscillating.

    Hi Rolf,

    Welcome to E2E, thank you for your interest in our products.
    Could you please provide me more details about your issue?
    Regarding another device, You could use a Class-D Audio Amplifier, It has higher efficiency than a Class AB Audio Amplifier, you could have a look in our product folder in ti.com.

    Best Regards
    Jose Luis Figueroa
    Audio Applications Engineer | A-Team

     
     

    You received this notification because you subscribed to the forum.  To unsubscribe from only this thread, go here.

    Flag this post as spam/abuse.

  • 0 in reply to Rolf Binder
    TI__Mastermind 20085 points
    Rolf,

    In order to reduce the noise, you could add a capacitor of 0.1uF between the power supply and ground, besides you could change the input capacitors in a range of 0.1uF to 1uF because they are very big. Maybe this could help to solve your issue.
    Our Class-D Audio Amplifiers have a typical frequency switching of 250kHz.

    Best Regards
    Jose Luis Figueroa
    Audio Applications Engineer | A-Team
  • 0 in reply to José Luis
    Prodigy 10 points

    Hi;

    I observed similar problem as you specified. This is a challenging problem as TDMA digital frame/link protocol is striking the IC. Basically, any RF interference can be picked-up by the IC. The IC is not design with solid immunity strength and designer will require to protect it externally.

    What I did is implementing shield which grounded/returned to the main/star ground to battery.

    I have added selected ferrite bead (high Z across 100MHz-1.4GHz) and bypass cap (pF) at the Vcc, and input lines which are very close to the IC terminal.

    As a results, the TDMA noise or RF interference will be stop before entering the IC via any path (Vcc and input).

    Hope this will give you way out.

    Thanks

    Yusasmadi