ADC Voltage Reference Selection for K32

[aberger]

I am using the FRDM-K32L2B3 and trying to understand the voltage reference selection for the ADC.  

In the ADC Chapter, the SC2[REFSEL] bits provide the following options:

00	Default voltage reference pin pair, that is, external pins VREFH and VREFL
01	Alternate reference pair, that is, VALTH and VALTL . This pair may be additional external pins or internal sources depending on the MCU configuration. See the chip configuration information for details specific to this MCU
10	Reserved
11	Reserved

This seems to conflict with the information from 2.3.3 Analog reference options:

How can I select between the 3 options VREFH, 1.2V VREF_OUT, and VDDA?

[Ben_Xu1 · Accepted solution]

Hi @aberger,

VREFH pin can be used as filter capacitor pin for high precision 1.2V VREF_OUT. When 1.2V VREF is enabled, VREFH is 1.2V VREF_OUT. Also, when 1.2V VREF module is enabled, adding supply to VREFH pad, which is a dedicated 1.2 VREF_OUT pad, from external is prohibited. 

1. ADC0_SC2[REFSEL] = 00b, VREFV1 module disabled, ADC reference voltage is VREFH.

2. ADC0_SC2[REFSEL] = 00b, VREFV1 module enabled, ADC reference voltage is 1.2V VREF_OUT.

3. ADC0_SC2[REFSEL] = 01b, ADC reference voltage is VDDA.

Thanks & Regards,

Ben