i.MX25 ADC integrated reference voltage

[andreas81]

Hello,

with i.MX25 ADC it is possible to use the internal 2,5V reference voltage. I can't find any Information about the precision of this voltage in the datasheet. Does someone has information about that?

Background: We supply the VDD_tsc with 3,3V and the Vref of ADC also with 3,3V. But the precision of 3,3V Vref is not very high. So we like to use internal reference to get better performance with AUX ADC inputs. For the touch Screen the 3,3V supply is good enough

Does it cause any Problems, if  VDD_tsc is supplied with 3,3V and we use 2,5V internal reference for AUX ADC? Does I need to switch between internal and external reference for touch and AUX Inputs in our case?

Best regards,

Andreas

[Yuri]

  The accuracy parameters of the i.MX25 integrated ADC are described in details in
the AN3948, available on the i.MX25 Documentation web page:

http://www.freescale.com/files/dsp/doc/app_note/AN3948.pdf

  The ADC accuracy is described in terms of Differential and Integral non-
linearity and referenced to the full-scale voltage that is equal to the
reference voltage. So, the ADC conversion accuracy also depends on the reference
voltage stability. The i.MX25 ADC module incorporates the reference voltage
source of 2.5V, however, it is quite inaccurate (about +/- 5%). So, to achieve
maximum conversion precision, it is recommended to use an external high-
stability and low-noise reference voltage supply.