Lpc2000

Pieter Verstraelen wrote:

>Hello all,
>
>a hardware related question: the LPC2210 has a dual power supply: 1.8V
>core voltage and 3.3V for the I/O.  
>Is the power-on (and power-off) sequence of these 2 voltages critical?
>Will a 1.8V regulator behind the 3.3V regulator do the job? The 1.8V
>will be a little bit later during power-on.
>
>  
>
 From what I'd read from the LPC2106 datasheet, there is no spec for 
cycling those two voltages. However, if you read the Notes (note 3) 
under the "Static Charactoristics" it says that application of a 5v 
signal to a tolerant pin is to be done with 3.3v supply present.

So, that infers that cycling of the 3.3v vs. 5v supplies is in order.  
Normally, you can accomplish this by feeding the 3.3v regulator from the 
5volt supply.   Then, ensure that no large capacitors within the 3.3v 
supply circuit would delay the rise / activation of the 3.3v output.  
Keeping capacitance to a reasonable level would accomplish this.  The 
only time that you could run into a problem there is if you use 
independant supplies for 3.3v and 5v.

I use a 3.3v regulator feeding a seperate 1.8v regulator.  So, the 1.8v 
stabilizes before the 3.3v and the 3.3v dies before the 1.8v.  The 1.8v 
is feeding the ARM core and the 3.3v is for the external logic 
interface. Following logical flow of the powerup / power down sequencing 
of supplies would be that the 1.8v core would be active before and after 
the 3.3v stabilization / decay.  I would suspect, that internally 
reverse biasing the 1.8v core via the 3.3v could be a "bad thing"?  :-P



>We bought a development board from Phytec and that board contains a
>bunch of components to adjust the power-on sequence.  The datasheet of
>the LPC2210 does not mention any potential problems or limits between
>the 2 supply voltages.  So I wonder why Phytec did go through the
>troubles of placing the extra components...
>
>  
>
It sounds like they designed an "end-all-be-all" solution that 
"one-size-fits-all".
Overdesign can be such a seductive thing...  ;-)

Regards,

TomW



-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------