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TAS5630 EVM PBTL vs datasheet PBTL

Russell May
Intellectual 685 points
Other Parts Discussed in Thread: TAS5615, TAS5630

PBTL operation is obtained from the EVM by paralleling outputs after the final filters. PBTL operation per the IC datasheet is obtained by paralleling IC outputs before the final filters, which requires fewer filter components. But the 1.0uF filter caps shown in the datasheet  are different from the 0.68uF caps in the EVM's. Is the difference important? So far I have only dealt with EVM's but I have to submit a real design soon.

To complicate the question more: I do not need all of the output power possible from a TAS5630, so I anticipate using larger filter inductors (15uH per TAS5615 datasheet and EVM, versus 7uH per TAS5630 datasheet and EVM). In that case, would the difference in filter caps be important? I prefer to use 0.68uF WIMA caps because they are substantially smaller than 1.0uF WIMA caps.

  • 0
    Intellectual 685 points

    To clarify my statement "paralleling IC outputs before the final filters": what I meant is "paralleling the inductor outputs before the final filters".

    I prefer to use the datasheet PBTL connections because it eliminates several filter resistors and capacitors.


  • 0 in reply to Russell May
    TI__Guru**** 189399 points

    Hi, Russell,

    Figure 15 of the d/s for the TAS5630 recommends connection after the LC filter. Well, I guess we combine the C, but I don't think that's what you meant.

    We have an app note that talks about designing LC filters for class-D amps: http://www.ti.com/litv/pdf/sloa119a

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 685 points

    PBTL operation with an EVM puts two RC filter networks in parallel ({C37,C52,C40,C41,R33-C44,R34-C45} and {C38,C39,C42,C43,R35-C46,R36-C47}), with two pairs of inductors driving each network. Effectively the capacitances are doubled and the resistances are halved. The TAS5615 and TAS5630 datasheets show only one such identical (or nearly identical) RC network for PBTL operation. But they are not quite identical:

    The RC filter networks for the TAS5615 EVM are the same as those in the TAS5615 datasheet; but caps {C37,C52} or {C38,C39} for the TAS5630 EVM are different from equivalent caps for PBTL operation in the TAS5630 datasheet. Why is there a difference?

    I cannot do a good calculation of what L and C "should be" according the the app note because (1) PBTL  operation is not mentioned in the app note and (2) this is not an audio application. The load is unpredictable, mostly capacitive, and can vary dynamically and wildly. Fortunately we are only interested in 50, 60, and 400Hz basic signals but we have to deal with potentially destructive feedback from load transients. Our application might be a misapplication, but the TAS5615 with suitable protections and accommodations is the best solution I have seen. Too bad it is Not Recommended For New Design (obsolete). The TAS5630 is not quite as good because it has about 2 Vrms less usable output voltage, but it seems better than the amplifiers we have built previously.