Re: eQADC operation on MPC5554

Allan,
  Actually the data was best near VHR approximately 0.2v error and 
worst at 1V with 0.900v error.  The problem has been solved however.  
We found that a high impedance was inserted in the VRL line due to a 
wiring error.  Shorting across the high impedance corrected the 
problem.  Thanks.  Do you have a link to EB643 you mentioned?  I 
cannot find it on the freescale website.
Joe
--- In [email protected], "Dobbin Allan-r11834" 
<Allan.Dobbin@...> wrote:
>
> Oh, I had expected that would have been the issue.
>  
> On reading your post again, I don't quite understand - to clarify - 
you
> are performing ADC conversions and the digital result is always off 
by a
> constant factor?  Could you provide some examples of the raw data 
and
> the input voltage.  Does your result clip out at 0 anywhere below 
0.9V?
>  
> Please verify you have VDDA0 and VDDA1 at 5V, Vrh at 5V, Vrl at gnd.
>  
> Other things to try - perform conversions on the internal refs to 
see if
> they are correct, perform conversions using both ADCs to see if 
both are
> the same, perform without calibration incase you have made an error 
in
> the MAC settings.
>  
> - Allan
> 
> ________________________________
> 
> From: [email protected] [mailto:[email protected]] On 
Behalf
> Of JVB1_wow
> Sent: Tuesday, November 14, 2006 2:12 PM
> To: [email protected]
> Subject: [MPC500] Re: eQADC operation on MPC5554
> 
> 
> 
> Allan,
> We have only the 100nF cap not the resistor.
> Joe
> --- In [email protected] <mailto:MPC500%40yahoogroups.com> ,
> "Dobbin Allan-r11834" 
> <Allan.Dobbin@> wrote:
> >
> > What do you have connected to the REFBYPC pin? You should only 
> have a
> > 100nF cap to gnd, not a resistor. See EB643 - the resistor was 
only
> > required on very early revs of silicon.
> > 
> > - Allan
> > 
> > ________________________________
> > 
> > From: [email protected] <mailto:MPC500%40yahoogroups.com>
> [mailto:[email protected] <mailto:MPC500%40yahoogroups.com> ] 
On 
> Behalf
> > Of JVB1_wow
> > Sent: Tuesday, November 14, 2006 11:37 AM
> > To: [email protected] <mailto:MPC500%40yahoogroups.com> 
> > Subject: [MPC500] eQADC operation on MPC5554
> > 
> > 
> > 
> > Hello,
> > I am designing a system with the MPC5554 micro-controller. We are
> > planning on using the eQADC. Checkout of the prototype hardware 
> shows
> > a large offset voltage of around -0.900V. The measured data in
> > perfectly linear just offset by this bias. Anyone seen this 
before? 
> > Thanks.
> > 
> > Joe
> > 
> > 
> > 
> > 
> > 
> > 
> > [Non-text portions of this message have been removed]
> >
> 
> 
> 
>  
> 
> 
> [Non-text portions of this message have been removed]
>