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Power for the OKI ARM mcus

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  • redsp@yahoo.com
    I am designing a low power controller for a DSP board and I needed a power circuit that would generate the 3.3 and 2.5 volt supplies the MCU needs. This also
    Message 1 of 3 , Feb 18, 2004
      I am designing a low power controller for a DSP board and I needed a
      power circuit that would generate the 3.3 and 2.5 volt supplies the
      MCU needs. This also needed to be as efficient as possible, but cost
      and size are both issues. The circuit I ended up selecting is a
      switcher, but not an inductive switcher. TI makes the TPS60500 family
      of switched capacitor stepdown regulators that automatically configure
      the topology to optimize efficiency. 3.3 volts is two thirds of 5
      volts and 2.5 is half of 5 volts. Turns out you can configure a
      switched capacitor converter to generate an output at 1/2 Vin, 2/3 Vin
      or 1/3 Vin using the same components. So this circuit generates 3.3,
      2.5 or 1.67 volts very efficiently.

      There are some losses in the switches, so it helps if the input
      voltage is just a bit higher than 5 volts or the outputs are just a
      bit lower than 1/2, 2/3, or 1/3 Vin. But according to TIs data and my
      tests, they work quite well at up to 100 mA or so, depending on the
      exact input and output voltages.

      You can get capacitors in 0805 packages up to 22 uF at 6.3 volts. So
      this circuit can be very small. I have not been able to find an
      inductive switcher this small or cheap.

      So if efficiency is important, check out the TPS60500.

      You can also power the Philips line of ARM controllers this way, but
      the 1.8 volt output loses a bit of efficiency. Still it is twice as
      efficient as an LDO. :)
    • skykotech
      ... cost ... family ... configure ... Vin ... 3.3, ... my ... Hi Rick, thanks for starting this group. If you were interfacing an SDRAM to the OKI part, what
      Message 2 of 3 , Feb 18, 2004
        --- In OKI-ARM-mcus@yahoogroups.com, redsp@y... wrote:
        > I am designing a low power controller for a DSP board and I needed a
        > power circuit that would generate the 3.3 and 2.5 volt supplies the
        > MCU needs. This also needed to be as efficient as possible, but
        cost
        > and size are both issues. The circuit I ended up selecting is a
        > switcher, but not an inductive switcher. TI makes the TPS60500
        family
        > of switched capacitor stepdown regulators that automatically
        configure
        > the topology to optimize efficiency. 3.3 volts is two thirds of 5
        > volts and 2.5 is half of 5 volts. Turns out you can configure a
        > switched capacitor converter to generate an output at 1/2 Vin, 2/3
        Vin
        > or 1/3 Vin using the same components. So this circuit generates
        3.3,
        > 2.5 or 1.67 volts very efficiently.
        >
        > There are some losses in the switches, so it helps if the input
        > voltage is just a bit higher than 5 volts or the outputs are just a
        > bit lower than 1/2, 2/3, or 1/3 Vin. But according to TIs data and
        my
        > tests, they work quite well at up to 100 mA or so, depending on the
        > exact input and output voltages.
        >

        Hi Rick, thanks for starting this group.

        If you were interfacing an SDRAM to the OKI part, what would you do
        for the 3.3 volt supply to the SDRAM? I know they can draw quite a
        bit of current during burst operations...

        Rick
      • redsp@yahoo.com
        ... Yes, but the current scales with operating frequency. With a max freq of 60 MHz, they should be in the range of 60 mA or so which is not out of reach of
        Message 3 of 3 , Feb 19, 2004
          --- In OKI-ARM-mcus@yahoogroups.com, "skykotech" <rick@s...> wrote:
          > Hi Rick, thanks for starting this group.
          >
          > If you were interfacing an SDRAM to the OKI part, what would you do
          > for the 3.3 volt supply to the SDRAM? I know they can draw quite a
          > bit of current during burst operations...
          >
          > Rick

          Yes, but the current scales with operating frequency. With a max freq
          of 60 MHz, they should be in the range of 60 mA or so which is not out
          of reach of the TPS60500. The current draw is spikey with large
          transients at the times of activity and much lower currents when not
          being accessed. The frequency of operation is much higher than the
          switching freq of the 60500. So using a larger cap on the Vdd rail
          will help to supply current to the SDRAM when being operated.

          The worse that will happen when the 100 to 150 mA boundary is crossed
          is that the TPS60500 will act as an LDO and not give you the better
          efficiency. But you need to consider the power being
          dissipated in the little MSOP10 package.

          Actually, we *will* have a single 16 bit wide SDRAM on the OKI part as
          an option on our boards. It will not be needed for normal operations,
          but I wanted to allow for people to run a fancier OS like uCLinux.
          Our board will have to limit the SDRAM operation to 70C.
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