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TPS7B69: LDO Input Capacitor Size

Joyce Gao
Intellectual 2970 points
Part Number: TPS7B69
Other Parts Discussed in Thread: , TPS7B84-Q1

Hi expert,

Customer is considering our TPS7B69 but have very limited board size. They claim that using a 50V 10uF MLCC capacitor as 7B69's datasheet recommended is too large in size. (Only 1210, 1206 package available for such specs)

  • I've advised customer using 4.7uF in 0805 package but they concern there will be risk. They've used a 1uF input capacitor for TPS7A66 and met problems.
  • I've also recommended TPS7B84 which recommends using only a 1uF input capacitor in datasheet which could reduce the size.

Do you have any other suggestions? It would be really great if we could solve this concern on both stability and layout size.

Many thanks!

  • 0
    TI__Guru 50025 points

    Joyce,

    You are referring to the input cap and not the output, correct? The amount of input capacitance required TPS7B69-Q1 for the application depends mostly on how far away the device is located from the main supply to counteract parasitic inductance of the power path. This device is stable with a small input cap (typical recommended is 0.1uF), so it will be stable with less than 10uF, but if there is a lot of parasitic inductance then there could be extra noise on the line. If stability is the concern then they should be fine using 4.7uF. 1uF should even be fine with regards to stability. 

    TPS7B84-Q1 would also be a good alternative because it is also stable with a small input cap. However, the issue of having the device located far from the main supply is the same, so a larger cap could be required to counteract reactive impedance on the main supply anyways, but for stability 1uF is enough. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Intellectual 2970 points

    Nick, yes it's the input capacitor, that's clear enough and many thanks!

  • 0 in reply to Joyce Gao
    TI__Guru 50025 points

    Sure thing!