MSP430F5325: MSP430F5325 - VREF+ with an external capacitor

Hi Joerg,

For external capacitor for Internal reference, you only need to support the internal reference with an external capacitor (such as 100pF) if you are making the reference voltage available at the pins (i.e., setting REFOUT = 1). When REFOUT = 1, The reference voltage is buffered and output to the VREF+ or VREF- pins. In this configuration, the reference must drive an external load and the capacitance at the terminal. To ensure settling and performance, decoupling capacitors are required. When REFOUT = 0, the reference is used only internally by the ADC12 module. In this case, the reference is buffered locally inside the ADC, and an external capacitor on the pin is not required for the internal conversion process itself.

For register settings confirmation, your proposed register sequence is generally correct for transitioning control from the legacy REF module to the newer ADC12 reference.

Hi Pengfei, 

Thank you for your explanations.

I would be interested to know if it is always better to use this external capacitor for ADC accuracy?
Does this also apply to e.g. low ADC clock and relatively long sample-and-hold times?

Regards Joerg

Hi Joerg,

It is recommended to use an external capacitor on VREF pins if you set REFOUT as 1.

A longer sample-hold time is trying to improve ADC accuracy by getting a more stable input voltage, but the capacitor in VREF pin is trying to improve accuracy from reference side.