Forums

voltage regulator configuration

Started by kalyanamsaritha June 13, 2008
Hi,

I have a power requirement for +5V, +3.3V and +1.8V.

Studying available designs, I have seen both parallel and series
configuration.

1. Series

+5V DC input with voltage regulators connected in series to convert +5V to
+3.3V, and +3.3V to +1.8V

2. Parallel

+5V DC input to +3.3V output, and +5V DC input to +1.8V output.

In both cases, all three voltages are available.

What are the pros and cons?

Also, in the Olimex schematic (top right corner), I see a Schottky Barrier
being used (BAT54C),
http://www.olimex.com/dev/images/ARM/ATMEL/SAM9-L9260-REV-B-sch.gif

I believe the main purpose was to isolate the +5V, +3.3V and +1.8V power
rails. Is this really required?

Thanks,
Saritha.


On Jun 13, 4:08 pm, "kalyanamsaritha" <kalyanamsari...@gmail.com>
wrote:
> Hi, > > I have a power requirement for +5V, +3.3V and +1.8V. > > Studying available designs, I have seen both parallel and series > configuration. > > 1. Series > > +5V DC input with voltage regulators connected in series to convert +5V to > +3.3V, and +3.3V to +1.8V > > 2. Parallel > > +5V DC input to +3.3V output, and +5V DC input to +1.8V output. > > In both cases, all three voltages are available. > > What are the pros and cons? > > Also, in the Olimex schematic (top right corner), I see a Schottky Barrier > being used (BAT54C),http://www.olimex.com/dev/images/ARM/ATMEL/SAM9-L9260-REV-B-sch.gif > > I believe the main purpose was to isolate the +5V, +3.3V and +1.8V power > rails. Is this really required? > > Thanks, > Saritha.
Both of your questions will be answered when you determine what power sequencing you need. The 1st when you know the power-up sequence, and the 2nd when you know the power-down sequence. G.
On Fri, 13 Jun 2008 18:08:26 -0500, "kalyanamsaritha"
<kalyanamsaritha@gmail.com> wrote:


>Also, in the Olimex schematic (top right corner), I see a Schottky Barrier >being used (BAT54C), >http://www.olimex.com/dev/images/ARM/ATMEL/SAM9-L9260-REV-B-sch.gif > >I believe the main purpose was to isolate the +5V, +3.3V and +1.8V power >rails. Is this really required?
It's probably there to protect the regulators from being "upside down" when securing the device. That is, if the input of the regulators gets shorted to ground when pulling out the power plug, the capacitors on the output (regulated) side of the regulator will discharge back through the regulator to the input. That's a Bad Thing. IIRC there is a small internal diode to accommodate some transients but a larger, external diode gives a bit more protection. -- Rich Webb Norfolk, VA
>Both of your questions will be answered when you determine what power >sequencing you need. The 1st when you know the power-up sequence, and >the 2nd when you know the power-down sequence. > >G.
Here is some info on power-up sequencing ... << snip >> There is no specific sequence to power up an AT91 microcontroller. Either the core voltage or I/O voltage can be powered first without any risk of destruction. However, Output values and power consumption are not guaranteed during power up sequence. We advise to perform a product specific reset after stabilization of supplies to have a known state. Although only one voltage rail can be supplied without any risk of destruction, correct functionality of the device cannot be guaranteed.