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Hello,
I'm driving the analog input signal beyond the reference rail of the ADS5421. My reference voltages are as follows:
VREFT = 3.5V (Externally driven with unbuffered series reference)
VREFB = 1.5V (Externally driven with op-amp buffered reference)
CM = 2.5V
The single ended voltage at the analog input pin (IN - PIN59) is a pulse with amplitude ~= 3.7V. I'm noticing that the preceeding sample dips negative. Is this expected operation when driving the analog input beyond the reference rails?
Also, what are the min/max limits that we can drive VREFT and VREFB at? Would it be possible to source VREFT with 3.9V and VREFB with 1.1V?
Don
Hi Don,
The only documentation that we have for the ADS5421 is the datasheet.
On page 3, the datasheet states that the difference between VREFT and VREFB must not exceed 2.025V,
so setting VREFT and VREFB to 3.9V and 1.1V, respectively, should not be done. Additionally, Table 1 on page 13, states the acceptable voltage for both references.
Setting these references beyond the published levels may damage the device, or cause unpredictable results.
With other ADCs that have external voltage references, I have seen harmonic distortion increase as the reference threshold is exceeded, but I'm not certain as to why you would be seeing an negative sample.
Hope this helps.
Best Regards,
Dan
Thanks Dan,
One more question.