Re: Power IC instead of MC33394

Can I just add that we now have production boards going through, using virtually the same distributed power supply circuitry as described by David Brown. We use the 5V on board supply to generate the 2.6V for the uP and 3.3V for logic and Flash Memory and we too have had no troubles at all in this department. I should say that we are not using CAN.
Cavan Orwell
  ----- Original Message ----- 
  From: David Brown 
  To: [email protected] 
  Sent: Tuesday, August 09, 2005 10:44 AM
  Subject: Re: [MPC500] Power IC instead of MC33394


  > Is there a IC instead of MC33394 from Freescale?
  >

  The simple answer is no.  There may be a slightly more complex answer if you
  already have a design built using the MC33394 - contact your Freescale
  distributer for information.  If you are in the position to need the complex
  answer, your distributer should probably already have contacted you.  Sorry
  for the cryptic answer here - it's just I don't know how much information
  about this is NDA.

  By far the most sensible and practical solution is to forget the MC33394
  ever existed, and build your own replacement.  The main features  of the
  MC33394 that you need to replicate are:

  The CAN driver - use a standard 82c250, or similar.

  The reset circuit - use a Dallas/Maxim 3-pin reset device on POReset, and
  tie HReset and SReset to 5V through a resistor.  The MPC5xx have perfectly
  good reset circuitry built-in.

  The power supplies and regulators are the main function of the chip, with
  one of it's key selling points being the correct power-up and power-down
  supply sequencing on 5V and 2.6V.  However, using seperate components is in
  fact extremely simple - use a 5V switch-mode supply (for efficiency - or a
  linear supply if you want smaller and cheaper and your main supply is not
  too high).  Use a low-dropout linear regulator to generate 2.6V from this 5V
  supply.  Your 2.6V will then rise correctly with the 5V.  Add a schottky
  diode from 2.6V to 5V to ensure that power-down sequencing is correct
  regardless of loads and capacitances on the two supply lines.  If you need
  3.3V, use the same arrangement as for the 2.6V supply.

  We changed over to this arrangement on a design, and it has worked
  flawlessly.  Compared to our original MC33394 design, it is cheaper, more
  efficient, has a much smaller in-rush current at startup, it's more reliable
  (sometimes the old solution had trouble at startup), has better thermal
  properties (the heat is more spread out), and avoids the daft arrangement
  with high-speed CAN lines mixed up with the power supply.

  Hope that helps both you and anyone else on the list.

  mvh.,

  David




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