Is external capacitor required for use of internal Vref on KL03?

[tedmawson]

I have a new design using an MKL03Z32CAF controller.  I want to use the internal bandgap voltage reference to calibrate my A2D against a Vdd that will fall as the CR2032 battery discharges.  I had assumed that I could use the bandgap Vref internally but it now seems that I may have to assign VrefOut to one of the pins and connect a capacitor to that pin. 

Questions:

1.     Is the external VrefOut pin - with capacitor connected - essential to the use of the internal bandgap Vref?

2.     Are there other ways to get accurate A2D readings given that my Vdd (used as Vref) could vary between 3.2 and 2.6 volts?

Thanks

[xiangjunrong]

Hi, Ted,

This is my opinion, the Voltage Reference module and the bandgap module are two independent modules, the bandgap module provides a standard voltage for the voltage reference module. The Bandgap module voltage can be tested by the ADC0_AD27 channel.

If you do not need the Vref_out pin output voltage, and the Voltage Reference module is disabled, you just need to test the bandgap voltage by ADC, in the case, you do not need connect a capacitor for the Vref_out pin. The Bandgap voltage is not dependent on the VDD or VDDA voltage.

If you need Vref_out pin output and enable the Voltage Reference module, plan to use it as ADC reference voltage, you have to connect a capacitor for the Vref_out pin.

Hope it can help you.

BR

Xiangjun Rong