- voltage regulator configuration
- Posted by kalyanamsaritha on June 13th, 2008
Hi,
I have a power requirement for +5V, +3.3V and +1.8V.
Studying available designs, I have seen both parallel and serie
configuration.
1. Series
+5V DC input with voltage regulators connected in series to convert +5V t
+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 Barrie
being used (BAT54C),
http://www.olimex.com/dev/images/ARM...-REV-B-sch.gif
I believe the main purpose was to isolate the +5V, +3.3V and +1.8V powe
rails. Is this really required?
Thanks,
Saritha.
- Posted by ghelbig on June 14th, 2008
On Jun 13, 4:08 pm, "kalyanamsaritha" <kalyanamsari...@gmail.com>
wrote:
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.
- Posted by Rich Webb on June 14th, 2008
On Fri, 13 Jun 2008 18:08:26 -0500, "kalyanamsaritha"
<kalyanamsaritha@gmail.com> wrote:
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
- Posted by kalyanamsaritha on June 14th, 2008
Here is some info on power-up sequencing ...
<< snip >>
There is no specific sequence to power up an AT91 microcontroller. Eithe
the core voltage or I/O voltage can be powered first without any risk o
destruction.
However, Output values and power consumption are not guaranteed durin
power up sequence. We advise to perform a product specific reset afte
stabilization of supplies to have a known state.
Although only one voltage rail can be supplied without any risk o
destruction, correct functionality of the device cannot be guaranteed.
