ADC leakage current followup - TomW

Started by Sutton Mehaffey March 7, 2006
Tom,

Since Philips isn't responding / hasn't responded to my ADC leakage
question, as you said would probably happen, is it safe to say the
leakage at the AD0 channels is probably 4ua max?  If so, I may put in
extra circuitry to handle to slop in measuring battery voltage, or I
may just add another ADC to my board.  I had an ADC on an 8051 project
and it worked great.  I just thought that an onboard ADC would
eliminate extra parts.  Maybe not...

Sutton
	

An Engineer's Guide to the LPC2100 Series

Sutton Mehaffey wrote:

>Tom,
>
>Since Philips isn't responding / hasn't responded to my ADC leakage
>question, as you said would probably happen, is it safe to say the
>leakage at the AD0 channels is probably 4ua max?  If so, I may put in
>extra circuitry to handle to slop in measuring battery voltage, or I
>may just add another ADC to my board.  I had an ADC on an 8051 project
>and it worked great.  I just thought that an onboard ADC would
>eliminate extra parts.  Maybe not...
>
>  
>
I really couldn't say, the spec sheet just is that vague.  My board is 
only measuring the voltage drop across a 3.3K resistor.  They are being 
used for EOL Burg (security) Zones. 

The only thing I would suggest is to get in contact with the Field Rep 
for Philips and put the question to them.  They have to get you an 
answer of some kind, that is their job to support engineers designing 
with the hardware.

TomW
	-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------
	
Good idea.  I'll post any results from that avenue.  Thanks.

Sutton
	--- In lpc2000@lpc2..., Tom Walsh <tom@...> wrote:
>
> Sutton Mehaffey wrote:
> 
> >Tom,
> >
> >Since Philips isn't responding / hasn't responded to my ADC leakage
> >question, as you said would probably happen, is it safe to say the
> >leakage at the AD0 channels is probably 4ua max?  If so, I may put in
> >extra circuitry to handle to slop in measuring battery voltage, or I
> >may just add another ADC to my board.  I had an ADC on an 8051 project
> >and it worked great.  I just thought that an onboard ADC would
> >eliminate extra parts.  Maybe not...
> >
> >  
> >
> I really couldn't say, the spec sheet just is that vague.  My board is 
> only measuring the voltage drop across a 3.3K resistor.  They are being 
> used for EOL Burg (security) Zones. 
> 
> The only thing I would suggest is to get in contact with the Field Rep 
> for Philips and put the question to them.  They have to get you an 
> answer of some kind, that is their job to support engineers designing 
> with the hardware.
> 
> TomW
> 
> 
> 
> -- 
> Tom Walsh - WN3L - Embedded Systems Consultant
> http://openhardware.net, http://cyberiansoftware.com
> "Windows? No thanks, I have work to do..."
> ----------------
>
	
At 11:34 PM 3/7/2006 +0000, Sutton Mehaffey wrote:
>Since Philips isn't responding / hasn't responded
to my ADC leakage
>question, as you said would probably happen, is it safe to say the
>leakage at the AD0 channels is probably 4ua max?  If so, I may put in
>extra circuitry to handle to slop in measuring battery voltage, or I
>may just add another ADC to my board.  I had an ADC on an 8051 project
>and it worked great.  I just thought that an onboard ADC would
>eliminate extra parts.  Maybe not...

Well, if you can afford the cost/space for an external A/D you can 
certainly afford to add an op-amp as an external buffer.  As an example 
consider

http://www.national.com/pf/LP/LPV321.html

SOT-23 case 60nA max input bias current <0.40 qty 1000.  I'm sure there are 
many others, such as the LMC7111 with an even lower input bias current in 
the same size package.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/