Forums

3.3V power supply on LPC2106 and USB

Started by Ezequiel L. Aceto October 28, 2005
Hello

I'm designing a little device with the LPC2106. I have worked with
this MCU but never in the situation that I wanted to work now.
I need to power the LPC2106 only with 3.3V, and also attach a FTDI232
USB (to program the LPC, and also as a virtual Comm for the PC).

One of the problems comes with the power supply for the LPC, can I
give 3.3V directly to the MCU, and connect a regulator to the 3.3V
line to generate 1.8V? I always connected 3.3V and 1.8V "in parallel"
as a 5V supply feed them, but now I only have 3.3V and don't know if
there is a problem to give first (for a few mSec) 3.3V and then 1.8V.

And last but not least, I need to power the FTDI with 3.3V, which is
not a problem, but I will only have 5V when connected to the USB, then
I will only have 3.3V. So I will connect and power VCCIO with 3.3V but
the other voltage sources will "float" when the device is not
connected. Might this cause any problem?

Thanks very much,
Ezequiel L. Aceto



An Engineer's Guide to the LPC2100 Series

Ez,

First off can I recommend that you consider using the 2138 in place of
the 2106. I started off with the 2106 and the only reason I would use it
now is because it has more RAM and possibly because it's a smaller
package. The 2138 has it's own 1.8V regulator and as you already have a
3.3V supply it means you can do without the size and cost of additional
regulators.

To answer your question though, yes, you can connect the 1.8V regulator
in series with the 3.3V without problems.

I am not sure about the FTDI question however, though there shouldn't
really be a problem as these types of chips are designed to be operated
this way. Personally, I find the CP2102 devices far easier to use as
they truly are a SCFF* single-chip USB-UART bridge.

*Small, Cheap, Fast, and Flawless (as far as I can tell).

*Peter* Ezequiel L. Aceto wrote:
> Hello
>
> I'm designing a little device with the LPC2106. I have worked with
> this MCU but never in the situation that I wanted to work now.
> I need to power the LPC2106 only with 3.3V, and also attach a FTDI232
> USB (to program the LPC, and also as a virtual Comm for the PC).
>
> One of the problems comes with the power supply for the LPC, can I
> give 3.3V directly to the MCU, and connect a regulator to the 3.3V
> line to generate 1.8V? I always connected 3.3V and 1.8V "in parallel"
> as a 5V supply feed them, but now I only have 3.3V and don't know if
> there is a problem to give first (for a few mSec) 3.3V and then 1.8V.
>
> And last but not least, I need to power the FTDI with 3.3V, which is
> not a problem, but I will only have 5V when connected to the USB, then
> I will only have 3.3V. So I will connect and power VCCIO with 3.3V but
> the other voltage sources will "float" when the device is not
> connected. Might this cause any problem?



Hi,
why not using the LPC214x, that has all the benefits of the LPC2138
plus USB on-chip. Programming through USB directly though is not
supported yet, may be Philips should come up with a solution there.
In regards to your 3.3V first followed by 1.8V is not a problem.
Usually these regulators follow the rising edge of the 3.3V fairly
quickly and by the time you reach 3.3V the 1.8V are there as well.
Bob

--- In lpc2000@lpc2..., Peter Jakacki <peterjak@t...> wrote:
>
> Ez,
>
> First off can I recommend that you consider using the 2138 in place of
> the 2106. I started off with the 2106 and the only reason I would
use it
> now is because it has more RAM and possibly because it's a smaller
> package. The 2138 has it's own 1.8V regulator and as you already have a
> 3.3V supply it means you can do without the size and cost of additional
> regulators.
>
> To answer your question though, yes, you can connect the 1.8V regulator
> in series with the 3.3V without problems.
>
> I am not sure about the FTDI question however, though there shouldn't
> really be a problem as these types of chips are designed to be operated
> this way. Personally, I find the CP2102 devices far easier to use as
> they truly are a SCFF* single-chip USB-UART bridge.
>
> *Small, Cheap, Fast, and Flawless (as far as I can tell).
>
> *Peter* > Ezequiel L. Aceto wrote:
> > Hello
> >
> > I'm designing a little device with the LPC2106. I have worked with
> > this MCU but never in the situation that I wanted to work now.
> > I need to power the LPC2106 only with 3.3V, and also attach a FTDI232
> > USB (to program the LPC, and also as a virtual Comm for the PC).
> >
> > One of the problems comes with the power supply for the LPC, can I
> > give 3.3V directly to the MCU, and connect a regulator to the 3.3V
> > line to generate 1.8V? I always connected 3.3V and 1.8V "in parallel"
> > as a 5V supply feed them, but now I only have 3.3V and don't know if
> > there is a problem to give first (for a few mSec) 3.3V and then 1.8V.
> >
> > And last but not least, I need to power the FTDI with 3.3V, which is
> > not a problem, but I will only have 5V when connected to the USB, then
> > I will only have 3.3V. So I will connect and power VCCIO with 3.3V but
> > the other voltage sources will "float" when the device is not
> > connected. Might this cause any problem?
>