View source for LPC1768 ADC ISSUES

*http://gvworks.blogspot.gr/2011/03/lpc1768-adc-has-too-many-glitches.html
*http://forums.nxp.com/viewtopic.php?t=5575
*http://permalink.gmane.org/gmane.comp.hardware.arm.lpc2100/55416
*[http://mbed.org/users/bobanderson/code/AnalogInAnalyzer/docs/tip/main_8cpp_source.html Bob Anderson AnalogInAnalyzer at mbed]
*http://code.google.com/p/cortex-m3-tutorials/downloads/detail?name=ADC_glitch_remove.rar&can=2&q=
*http://www.digipedia.pl/usenet/thread/13010/13828/
 I experimented by adding a capacitor from adc in to Vref- and 2.2nF ceramic 0805 close to the pins cure the problem.
 ....
 The circuit I suggested cured the problem. You can experiment with the R and C values but try starting with something like 100 ohms and 470pf.
<cpp>
It has to be the software. I have the ADC in my LPC1766 measuring 8 CHs of
voltages,
and I get 0.05% accuracy or better every read consistently.
I am measuring +5.0V, +12V, -12V, +48V through simple R dividers and 1
inverter opamp.
My source impedances to the ADC vary from 500 to 5K Ohm.
My Vref is nothing but a simple dual RC lowpass of 10Ohm/0.22uF from the
3.3V.
Full Scale factor for each supply is set to about 3.0V (90%) of the 3.3Vref
span.
Nothing fancy at all.

The only variations I see are in the actually DC voltages, which the ADC
accurately reflects.

I have even switched the ADC clk freq around, don't see much difference even
then.

Now if I don't have the code setup right, I can get totally wild readings
back from the ADC.
I would suggest you try different ADC code and see what happens.

Perhaps the Pin I/O settings are not correct. Or there is something else
wrong.

I really think the problem must be somewhere in your code.
I've never had problems with ADCs in any NXP MCUs.
It's not the chip.

Chris.
</cpp>
[[Category:All]]
[[Category:Mbed]]