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DCDC buck converter output capacitor placement

Discussion in 'Electronic Design' started by [email protected], Jun 15, 2013.

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  1. Guest

    I have a microprocessor with built in DCDC converter. We need to provide inductor and output capacitors externally at the respective pins of the processor. The regulated o/p from the internal DCDC converter is for internal core and IO as well as for external peripherals. The manufacturer recommends using 0.01uf, 0.1uf, 1uf and 33uf at the DCDC output pin. What should be the order of placement of these o/p capacitors on the board? 0.01uf close to the pin and 33uf away or the other way? The current from the o/P pin is both ways. i.e goes internal to the IC as well as goes out of the pin to the other peripherals on the board.

    -bjnk
     
  2. Joerg

    Joerg Guest

    Smallest capacitance closest to the pin. But nowadays a 0.1uF in 0603
    package is good enough, there is usually no need for an extra 0.01uF.
    The 1uF is debatable, may not be needed if the 33uF is a ceramic.
     
  3. Guest

    I wonder why?

    I remember working a zigbee chip years ago, it had an on-chip LDO
    since it the chip was 1.8V and usually it would run on a ~3V battery

    everyone looked at me funny when I suggested adding a buck converter,
    it was really only a matter of adding a switch on chip and an external
    coil
    and diode it didn't have to be very accurate and in sleep mode where
    the chip only used uA the switch could just be permanently on since it
    would
    be feeding the LDO

    I know it got put in, but I don't know how well it worked


    -Lasse
     
  4. Guest

    Thanks. Its i.mx23 from freescale.
     
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