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TI Home » TI E2E Community » Support Forums » Amplifiers » Audio Amplifiers » Audio Amplifiers Forum » Voltage spikes on startup TAS5518C
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Voltage spikes on startup TAS5518C

This question is answered
Egbert Boer
Posted by Egbert Boer
on Mar 21 2012 14:38 PM
Prodigy70 points

I have designed a full digital amp using the TAS5518C.

When i power up the amplifier the output "Valid" of TAS5518C gives a spike which activates the output devices making "cracking" noise i the speakers.
This spike also appears when the reset pin is pulled low.
I there a simple fix of do i need to add more circuitry to filter the spike?

Thanks Egbert

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  • Tuan Luu
    Posted by Tuan Luu
    on Mar 21 2012 14:56 PM
    Mastermind25875 points

    Hello Egbert:

    In some devices, there may be a glitch in the logic where VALID signal is not being held low during power on.  To keep everything quiet, you may want to add a pre-bias circuit on VR_PLL (internal 1.8V regulator) - 3.3V to 60.4 kOHm resistor to pin 11 (VR_PLL), pin 11 to 49.9 kOhm resistor to ground and 0.01uF cap from pin 11 to ground.  This will help your power up noise. 

    Best regards,

    Tuan

    Audio Applications

    Texas Instruments, Inc.

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  • Egbert Boer
    Posted by Egbert Boer
    on Mar 22 2012 11:13 AM
    Verified Answer
    Verified by Don Dapkus
    Prodigy70 points

    I have tried your suggestion but it did not solve the problem.
    Instead i have added a pre-bias circuit on the vr_pwm pin using : 3,3v > 47k > vrpwm > 56k + 100n > ground.
    This solved the problem, can this circuit inject any noise?

    I also figured out I need a brown-out detection, and pull the reset line low as soon as it is detected.
    This eliminated the noise generated when the amp is turned off.

    Thank you for your help.

    Egbert

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  • Don Dapkus
    Posted by Don Dapkus
    on Mar 31 2012 17:26 PM
    Guru101635 points

    Hi, Egbert,

    Thanks for closing the loop with us on your solution!

    -d2

    -----

    Don Dapkus

    Audio Applications Engineering Manager

    Dallas, TX USA

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