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TPS7A4001: Schematic review

d_zero
Genius 4735 points
Part Number: TPS7A4001
Other Parts Discussed in Thread: PSEMTHR24EVM-081

Hi All,

please can you review our schematic with TPS7A4001 LDO

Vin = 56V

Vout = 3.3V

Iout = (12mA TPS23881RTQ + 11.3mA ISO1644DW) ~25mA max ; Iout_typ = 15mA

-> is one 10uF 25V 1206 X5R ( effective @ 3.3V -> 9.5uF) enough or should i leave the additional footprint C61 and populate it with 10uF 25V 1206 X5R?

-> on the input is 1uF 100V 1206 X7R (effective @ 56V -> 470nF) is this ok or do i need additional C66 to be populated with 1uF 100V 1206 X7R?

in TIDA-050026 there is similar configuration of LDO and only one 1uF 100V 1206 X7R is used

-> as the 56V comes from a isolated flyback converter do i need some LC or Ferrite bead filter on the input of TPS7A4001?

Best Regards,

David.

 

  • 0
    TI__Genius 12365 points

    Hi David, 

    The configuration looks ok. This device needs an effective capacitance of 4.7uF for the output, therefore, having 9.5uF should be sufficient. In the case that this is really a concern, perhaps adding a 1uF rather than a 10uF. 

    As for the input, the required minimum capacitance is 1uF, therefore, another cap is required, perhaps a 1uF||100nF with a 2.2uF. 

    How much ripple is expected from the flyback converter? 

    Best, 

    Edgar Acosta

  • 0 in reply to Edgar Acosta1
    Genius 4735 points

    Hi Edgar,

    if i use 1u || 1u || 100n then this is effective over 1uF, but how do you explain this TI reference design that has only 470nF effective capacitance on input?

    PSEMTHR24EVM-081 /  TIDA-050026 / PSIL081

    We expect 100mVpp like on this design

    https://www.ti.com/lit/ug/tidt115/tidt115.pdf?ts=1656057612473

    Best Regards,

    David.

  • 0 in reply to d_zero
    TI__Genius 12365 points

    Hi David, 

    Reference designs serve as a starting point and guidance to customers. 

    In addition, the reference design only shows a 1uF rated for 100V, although an estimation could be made, it is hard to tell how much it will de-rate without exact part number.

    It is common to see that a capacitor is selected with the exact minimum capacitance value. 

    With 100mVpp, you should be ok without any filter.

    Best, 

    Edgar Acosta

  • 0 in reply to Edgar Acosta1
    Genius 4735 points

    Hi Edgar,

    here is the PN from BOM 

    C46 4 1uF 12061C105KAT2A AVX CAP, CERM, 1 μF, 100 V,+/- 10%, X7R, 1206

    and VPWR is 55V

    Best Regards,

    David.

  • +1 in reply to d_zero
    TI__Genius 12365 points

    Hi David,

    Yeah, I looked at the capacitor and it will derate more than 50% @55V, closer to ~400nF, even lower than the 470nF estimation. 

    As previously mentioned, reference designs are to serve as guidance and not as a final product. 

    Just make sure enough capacitance is placed i.e 1uF||2.2uF||100nF or 10uF||1uF||100nF. It is recommended to use 10uF capacitor for better AC performance. 

    Best, 

    Edgar Acosta