Re: Power IC instead of MC33394

I use it for the 561.  If you look closely at the specs, the power
sequencing is not actually that hard.  You just have to ensure that the 5V
line is never more than a certain voltage (3.1, IIRC) about the 2.6V line,
and never more than a certain voltage below the 2.6V line, as well as
meeting usual power rise times.  Making 2.6V from an LDO linear regulator
taking its supply from the 5V line practically guarentees the power rise
sequencing, as long as your 5V rises sensibly.  You would have to try very
hard to make something that didn't work, such as massive capacitance on the
2.6V line and very little on the 5V line.  For power down, the sequencing
will also be satisfied, unless you have much more load compared to
capacitance on the 5V line (such that the 5V line drops quickly, while the
2.6V line stays up due to the capacitors).  The solution here is the
Schottky diode from 2.6V to 5V.

David


> Do you use your scheme for just the 555 or 565 as well. If 565, how do
you
> explicitly ensure the power up/down sequencing requirements of  the are
met?
>
>
> In a message dated 8/10/2005 9:32:39 AM Eastern Standard Time,
> [email protected] writes:
>
>
>
> Just to  second what David says really. We use individual regulators,
> switched mode to  get down to 5V (LM2595) then LDO (LM1117) to 2V6 and 3V3
if
> necessary. It all  works really well, the reset device is a SOT23  DS1818.
>
> Pete
>
> -----Original Message-----
> From:  [email protected] [mailto:[email protected]] On Behalf Of
> David  Brown
> Sent: 10 August 2005 13:12
> To: [email protected]
> Subject:  Re: [MPC500] Power IC instead of MC33394
>
>
> The power supply devices  were pretty standard devices we use on many
cards -
> I think the 5V switcher is  an LM2673, and the LDOs are LM1117 adjustable
> regulators.  The reset  device is a LM3724IM5-2.32, which I think is
National
> Semiconductor.  Of  course, you'll have to figure out the passive
components
> around the supplies,  depending on your source supply and your power
requirements.
>  I don't  think the exact components actually matter much - it's just a
> matter of  dimensioning them properly according to your board's needs -
extra
> ripple on  the supplies would not go down well with the MPC. And if you
need sleep
> modes  on your card, things are going to be more  complicated.
>
> mvh.,
>
> David
>




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