LPC4357 ADC reference: bandgap vs VDDA

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by rmcaleer on Tue Feb 24 15:57:06 MST 2015
I am hoping someone can explain the relationship between the internal ADC bandgap reference and VDDA on the LPC4357

The user guide (UM10503.pdf) documentation for the LPC4357 refers to an ADC bandgap reference: this can be output on PF_7
It also mentions VDDA as being the "Analog power supply and ADC reference voltage"
The datasheet LPC435X_3X_2X_1X.pdf describes the operation of the ADC being "full rail" with respect to VDDA.

I can see that using BGAP_SWITCH (on the POWER_CONTROL I can turn off the band gap)

In order to understand how these interact I have the following questions:
- how/where is the bandgap reference used?
- what is the voltage of the bandgap?
- what is used for ADC reference if I turn the bandgap off?
- if I connect the bandgap to PF_7 and turn it off could I provide an external reference?

Thanks for any help you can provide.

Best regards,