Hello,
I've used the the ADS1258 ADCs for a couple years now, but within the past 6-months - 1 year I've encountered an issue with these devices that I haven't been able to fully understand or resolve. The issue is that there is a mode in which the readings from this ADC will become offset by some value. This affects not just the analog readings going into the ADC but the value of the internal measurements, such as the Temperature and offset. I've been able to correlate entering the error mode with power draw for the system under test, though I don't believe it be a thermal issue.
My question: are there any known conditions that cause the ADS1258 to enter this mode that I might be missing? On a couple different PCBs we've tried different layout approaches to see if it was an electrical issue, but we've had no luck.
I'm providing an example dataset from one of the devices we have with this ADC on it. I use the ADS1258 to measure the temperature from small, 2W heaters. These heaters are used to warmup a sensor to a target operating regime, usually several hundred degrees Celsius. I have a dataset that shows an example of the issue that I've encountered. In the dataset, all the measurements (except for the microcontroller temperature) were calculated from values gathered by the ADS1258.
I can track whether I've entered this error mode by comparing the measurement of the ADS1258 Core Temp with our Microcontroller Core Temp. In this test, the ADS1258 enters the error state around t=140s and gets out of the error state around t = 430s.
I can correlate the ADS1258 entering the error state by turning on some of our heaters and leaving the error state by lowering the setpoint of one specific heater. Note that each heater is approx. 2W power consumption when at temperature. We control two of the heaters to a target temperature(Initially 550 °C and 450 °C for heaters 1 and 2) and two more heaters to a target resistance (HTR 3 and HTR 4 both to 8.8 ohms). During the test, we adjusted the heater 1 setpoint to 525 °C, and we believe this action to have returned the ADS1258 to a normal mode of operation. The sequence is:
1.) Turn on Heater 1 (T = 0s)
2.) Turn on Heater 2 (T = 90s)
3.) Turn on Heater 3 (T = 160s)
4) Adjust Heater 1 Setpoint to 525 °C (T = 430s)
5) Turn on Heater 4. (T = 480s)
Sensor 3 is an oxygen sensor, and we have it measuring percent concentration of O2 in a lab room, which will be around 21%. Note that the measurement of the sensor isn't considered accurate until around t=250s, when HTR3 has come to temperature. This sensor was calibrated with HTR1 unpowered and with the ADS1258 not in the error state. In this error mode, there is a 6% error induced on the calibrated measurement of the O2 sensor.
Thanks,
