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TPS782: TPS78230 maximum capacitance

Luis Filipe Rossi
Expert 1035 points
Part Number: TPS782

Is there any maximum capacitance (from ceramic capacitors) that should be used with a TPS78230? Datahseet just states a maximum ESR but not a minimum.

  • 0
    TI__Guru 55940 points
    We will respond on the next US business day.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Guru 55940 points
    Hi Luis,

    TPS782 was designed, characterized, and tested with battery operated applications in mind. As a result we did not focus on large capacitors. How large of a capacitor are you considering using?

    The largest capacitor I am aware of us testing the LDO with is 10uF; however, you should not have issues with larger. A few things to keep in mind when selecting a larger capacitor is that the active pull-down circuit will take longer to discharge the output and startup time will increase. You may also want to consider increasing the input capacitance to help with the increased inrush and to provide a prefilter.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Expert 1035 points

    Currently we are using 4.7uF capacitor right close to the TPS78230, one more 4.7uF in the middle of the board, a 22uF on the opposite corner of the board and several decoupling capacitors ranging from 100nF to 1uF.  The board is quite small (battery powered): 2.5x3.2 cm and it is a 4 layer board with dedicated VCC layer. All capacitors are ceramic. I was wondering if that 22uF capacitor might result in some instability as the board is very small and with a dedicated VCC layer the inductance and resistance would be very small. We tried to measure with an scope and I could not see anything meaningful. We use a MSP430 and we are having random (few boards with some weeks on the field) BROWNOUT and RST/NMI resets and I was wondering if that might be the cause.

  • 0 in reply to Luis Filipe Rossi
    TI__Guru 55940 points
    Hi Luis,

    I would not expect your capacitance to be causing any issues; however, scope shots of Vin, Vout, and if possible current would be able to rule out stability. It would be good if you can get this scope shot during a fault condition as it will also provide more information on the transients.

    You mention that your application is battery powered. Is the TPS782 powered directly off the battery or is there a boost circuit that allows you to use more of the battery voltage? Do you know anything about the battery voltage at the time of the brownouts and resets?

    Very Respectfully,
    Ryan