Tool/software:
Hi,
I am reviewing some of our MSP430I2040 based sensors and found out that SD24 ADC sometimes output negative readings when they are connected to known 0V input. In one instance, we connect a precision reference resistor and PT100 RTD in series (illustrated below), measures voltages across them before and after excitation current is turned on.
// SD24 configuration SD24CTL &= ~SD24REFS; // internal ref SD24CCTL0 |= SD24GRP | SD24DF | SD24SNGL; // Single sample, 2's complement SD24CCTL1 |= SD24GRP | SD24DF | SD24SNGL; SD24CCTL2 |= SD24DF | SD24SNGL; SD24INCTL0 = SD24GAIN_8; SD24INCTL1 = SD24GAIN_8; SD24INCTL2 = SD24GAIN_8;
Before excitation current is turned on, the baseline readings can look like something like the following:
// 2's complement 0xFFE9 // -23 0xFF55 // -171 0xFF96 // -106
Without excitation current, the expected the output from ADC should be 0 or some small positive numbers. So my question is, are those negative numbers we observe an indication of reverse current passing through the circuit? Or they just happen sometimes or on some MCU units?
Please advise, thanks.
ZL
