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TAS6424-Q1: the output capacitor and the feedback capacitor for TAS6424

Mamoru_Uozu
Prodigy 310 points
Part Number: TAS6424-Q1
Other Parts Discussed in Thread: TAS6424,

I have two question.

(1)

The TAS6424 datasheet shows the output capacitor is put on between out_1P and GND, out_1N and GND.

If I put the output capacitor on between out_1P and out_1N, what is the negative point and the benefits?

According to the apps note: http://www.ti.com/lit/an/slaa701a/slaa701a.pdf, it depend on what type of modulation.

Which modulation does TAS6424 have?

(2)

TAS6404 EVM is using 0.22uF for the feedback capacitor.

If I use 0.22uF for the feedback capacitor, what is the negative point and the benefits?

Thanks.

Mamoru Uozu

  • 0
    TI__Mastermind 34235 points

    Hello,

    1.  The TAS6424-Q1 modulation scheme is BD mode and requires the filter capacitors to ground. 

    2.  There are no feedback capacitors, maybe your are looking a the bootstrap capacitors.  Which capacitors are you referring to?   

  • 0 in reply to Gregg Scott
    TI__Prodigy 310 points

    Thanks for your response. Let me ask again.

    2. yes, i mean the bootstrap capacitors like BST1_P, BST2N.

    If I use 0.22uF for the bootstrap capacitors, what is the negative point and the benefits?

    Mamoru Uozu

  • 0 in reply to Mamoru_Uozu
    TI__Mastermind 34235 points

    Uozu-san,

    The bootstrap capacitor needs to be sized according to the lowest frequencies that are planned to used.  Since we use 100% modulation, we need to make sure the bootstrap voltage is maintained under worse case conditions.  The special condition can occur where the bootstrap may sag if the capacitor is not sized accordingly and the signal is just below clipping where the PWM is slightly less than 100% modulation with sustained low frequency signals.  The bootstrap may need to be up to 2.2uF when driving subwoofers that require frequencies below 30Hz.  The typical value is 1uf. A value of 0,22uF is too low.