ADC Vrefl benefit

[gam01hr]

Hallo,

I use the MC9S08LL16 device and the ADC. There are few pins associated with ADC: Vdda, Vssa, Vrefh, Vrefl and other. The Vrefl is usually tied to Vssa. I would like to know, what is it good for to have separated the Vrefl pin. Can its voltage level be externally 'shifted'? For example with voltage reference to 1.2V?

[Rick_Li]

Hi Martin Gazda,

As mentioned in the reference manual, Vrefh is the high reference voltage for the converter. In some package, Vrefh is connected internally to Vddad.

If externally available, Vrefh may be conected to the same potential as Vddad or

MAY BE DRIVEN BY AN EXTERNAL SOURCE BETWEEN THE MIN Vddad AND THE Vddad POTENTIAL. (page 149 of the below document)

http://cache.freescale.com/files/microcontrollers/doc/ref_manual/MC9S08LL16RM.pdf?fasp=1&WT_TYPE=Ref...

As in Characteristics,the Min of Vrefh is 1.8v. (p36 of below document)

http://cache.freescale.com/files/microcontrollers/doc/data_sheet/MC9S08LL16.pdf?fasp=1&WT_TYPE=Data%...

So, the Vrefh can be from 1.8v to Vddad.

Hope it helps!