Part Number: ADS1248 Dear Sir, My customer is testing ADS1248 using R6161 DC voltage generator to supply. The generator supplies 0mV to ADC input through INA129 , then monitor ADC digital output. An issue is that ADC output not zero but 1uV to 50uv depending on R6161 range setting 1V(divide=off) to 10mV(divider=on). It is supposed that there is some common voltage isolated between R6161 power ground and ADC DC ground. If both grounds are shorted, ADC output is zero volt (normal). It is also observed error voltage is reduced from 50uv to 3uV when data rate is changed from 40sps to 20sps. They checked same test for ADS1210 and it outputs no error voltage (zero volt output) in any conditions above. They checked bypassing INA129 but the error is still existed, so it looks ADC performance difference. Does CMRR less performance of ADS1248 cause this error? CMRR is min 80dB (at DC and G=1) for ADS1248 and min 100dB for ADS1210 . If so ADS124S06 has better CMMR (min 110dB) which might be much safer for testing with isolated ground CMV between DC generator and ADC? Best regards, Masa
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