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

It's good to know that this arrangement works for others, as confirmation of
the solution (I've also had our very capable EBV Freescale expert look at
the schematics).

We have two 82c250 CAN drivers on the board, using seperate CAN controllers
on the MPC561.  Loop-back tests at around 2.2 MBaud worked flawlessly - not
bad, considering the standard is only up to 1 MBaud.  But then, the 40 MHz
561 parts work fine up to around 90 MHz (at which point the UARTs get a bit
odd - the cpu core keeps going fine).


>   ----- 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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