KE06Z 64 pin version ADC reference

[ngiussani]

Hi,

I'm new to this community, so I'll start by introducing myself. I'm an Electronic Engineer from Argentina. I've been working with ARM core devices for around 10 years. Recently we selected the Kinetis K series microcontrollers (KE06Z, K02, K22, K60) for various applications.

I'm starting a design for a device that requires 5V supply, so I selected the KE06Z 64 pin version.

I'm not sure what's the idea with the VREFH for ADC. The Reference Guide says VREFH is internally connected to the VDDA pin, so I'm not able to connect an external reference. Is that so? Or am I misreading something?

I'm not sure if I can use as reliable reference source the internal bandgap, if I'm can't use an external reference.

Thanks in advance.

P.S.: I couldn't find anything like this in other discussion. If it was a subject of another one, my apologies.

[davidsherman]

It appears that VREFH is indeed connected to VDDA.  However, the analog supply VDDA can be +/- 100mV of VDD, so you could run that from a separate, more accurate supply voltage.  VREFH has limitations on other parts as well, it has to be at least half of VDDA on parts that don't have it internally connected.

[ngiussani]

Thank you David. I thought so. The thing is, I don't understand why would the chip designers make VREFL available to use instead of (in my opinion and experience) the much more useful VREFH.

I'm switching to the 80 pin version, that has VREFH available. However, I think it's a shame that the 64 pin version, which fitted my intended use, has this limitation.