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TPS7A78: Input Range

Brian Angiel
Expert 4370 points

Part Number: TPS7A78

Regarding TPS7A78, I see in the datasheet that the highlighted input voltage range is 70 to 270VAC. I understand that Cs and Rs affect the maximum AC supply voltage, so:

  • Can this device support 347 to 480VAC input with a specific Cs/Rs configuration?
  • On the other end, can it support 24VAC input?
  • If so, in either case, is there anything to be aware of regarding the performance/capabilities of the device?

Thanks,

Brian

  • 0
    TI__Guru 50190 points

    HI Brian,

    Please see my responses below:

    • Can this device support 347 to 480VAC input with a specific Cs/Rs configuration? *The only thing limiting the higher AC voltages are the high voltage capacitors themselves. The Cs capacitor is droping the high voltage and making an AC current source that we rectify and clamp. I recently found that Vishay has an MKP338 series which is rated to 440VAC but we have not tested these.
    • On the other end, can it support 24VAC input?*Here we run into the issue of the gap between pulse peaks. At 24VAC for 5VOUT, we need the SCIN pin to charge up to ~22V. We did not design this device to work well for 24VAC as tht would require a slightly different architecture. 
    • If so, in either case, is there anything to be aware of regarding the performance/capabilities of the device? *The primary concern is making sure your Cs is rated for your AC input and Rs is sized for the maximum clamp voltage of your MOV/TVS. This is VACCLAMPMAX/2.5A. If you already have circuitry clamping surges ahead of the TPS7A78, then Rs should be your peak AC voltage divided by 2.5A. (Our maximum recommended surge current into SCIN is 2.5A).

    One key point emphasized in the datasheet and user guide is that when you test full-bridge mode, do not try to probe with a grounded scope.

     

    I hope this answers your question. If not, please let me know.

     

    Regards,

     

    John