Other Parts Discussed in Thread: ADS8881, OPA333, REF5045, THS4131
Hi Team,
Here a summary of my findings on the REF5050:
- I am using the ADS8881IDRC ADC in one of my projects.
- To create the REF voltage I use the REF5050AIDR: pls. refer to the attached drawing for the ckt. details.
- The PVS DC supply level at the input of the REF5050 is set at 7.5VDC (actually it measures 7.55VDC); The ADS8881 is fed at 3.3VDC.
- I have taken the REF biasing ckt. from the ADS8881 Data Sheet as is, with the exception of the supply voltages to the OPA333, which is set to 5.25VDC (as this IC cannot work at the 7.5VDC supply): the ckt used to create the 5.25VDC is shown at bottom-left of the attached PDF.
- We have assembled 3 boards, and in all of them the REF5050 is putting out ~3.94VDC and not 5VDC as it should.
- I have checked everything possible and besides noticing that the ADS8881 data sheet recommended (??) REF IC for the ADS is the REF5045, I couldn't see any spec violations, yet the REF5050 outputs are wrong by much more than the specified accuracy of 15mV.
- The HVREF voltage is exactly what the half of the REF5050 output is, it is designed to be 2.5VDC and fed to the a THS4131/pin 2 as the Vocm, - as the ADS8881 does not provide it – in order to use max. available swing at the ADS8881, but of course, it is lower now.
Q1: Any ideas how to get the REF5050 to put out 5VDC output as it should???
Q2: Why is the REF5045 the recommended part to bias the ADS8881 – as shown above – any peculiar problems with the REF 5050 in this case? The Recommended Operating Range is OK with a nominal of 5VDC at the ADS8881 REF input:
Waiting for prompt reply,
Thanks,
Shlomi
