# Questions regarding ADS1243 (clock source, and Vref)

Hi Everyone

Could someone point me to an apropreate clock source for the ADS1243?

following crystals are suggested:

Crystal 2.4576 | 0-20pF | 0-20pF | ECS, ECSD 2.45 - 32
Crystal 4.9152 | 0-20pF | 0-20pF | ECS, ECSL 4.91
Crystal 4.9152 | 0-20pF | 0-20pF | ECS, ECSD 4.91
Crystal 4.9152 | 0-20pF | 0-20pF | CTS, MP 042 4M9182

However I have no idea what to base my choice on.

About Vref. Am I safe in simply connecting Vref+ to 5V and Vref- to GND ?

It says:

The external voltage reference is differential and is represented by the voltage difference between the pins: +VREF
and –VREF. The absolute voltage on either pin, +VREF or –VREF, can range from GND to VDD. However, the following
limitations apply:

For VDD = 5.0V and RANGE = 0 in the ACR, the differential
VREF must not exceed 2.5V.
For VDD = 5.0V and RANGE = 1 in the ACR, the differential
VREF must not exceed 5V.

What is RANGE ?

Thanks to anyone who can give me some advice.

Regards

p.

fkeel:
Could someone point me to an apropreate clock source for the ADS1243?
...
following crystals are suggested:

Crystal 2.4576 | 0-20pF | 0-20pF | ECS, ECSD 2.45 - 32
Crystal 4.9152 | 0-20pF | 0-20pF | ECS, ECSL 4.91
Crystal 4.9152 | 0-20pF | 0-20pF | ECS, ECSD 4.91
Crystal 4.9152 | 0-20pF | 0-20pF | CTS, MP 042 4M9182

However I have no idea what to base my choice on.

The point about using a frequency of 2.4576 or 4.9152MHz is that these frequencies give good rejection of 50Hz or 60Hz mains noise. If you go to the Farnell (Europe) or Newark (USA) site you will find a selection of crystals of these frequencies, see http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203436+110200502+110175016&Ntk=gensearch&Ntt=crystal&Ntx=mode+matchallpartial&No=0&getResults=true&appliedparametrics=true&locale=en_UK&divisionLocale=en_UK&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=2031+203436&mm=1002300||,1002729||,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D2031%2B203436%26Ntk%3Dgensearch%26Ntt%3Dcrystal%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D2031%2B203436. Pick one that is specified for a load capacitance in the range 15 to 20pF.

fkeel:
About Vref. Am I safe in simply connecting Vref+ to 5V and Vref- to GND ?

Yes, however you will need to set RANGE=1 to get sensible readings from the device.

fkeel:
What is RANGE ?

It is the value you program into bit 2 of register 02h. See page 16 of the datasheet.

thanks for the pointers. highly appreciated

p.