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TM4C1294NCPDT: AIN-16 unrelated switching noise
Part Number: TM4C1294NCPDT
Did not add in post AIN-16 is the last (configured) analog input but there are three more (AIN-17,18,19) on the end (PK1,2,3) respectively that will later be populated LM94022 and an analog control pot. So for now (PK1,2,3) circuit traces are disconnected via 0R near MCU pin or exist within 1/2" from MCU input.
Oddly AIN-16 (PK0) is on same GPIO port as M1/2Fault inputs (PK6, PK7) configured IN direction WPU. Those PCB traces direct couple to analog comparator outputs Co1,Co2 (PD1, PD2) more recently configured for OD direction. That seems to be another possible link to why the new LM94022 is behaving differently than the partially shorted output one. Saying shorted but in reality is 2.9k resistance to ground pin considered a short?
TI-Tina analysis plots of any analog comparator output switching noise may not be enough to trip MnFault inputs. Yet is it plausible switching noise is cross talking inside GPIO port K? and spilling onto AIN-16? Why is this scenario even occurring a more puzzling question but seemingly links to analog comparator being suspect.
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In reply to Gl:
In reply to Charles Tsai:
Charles TsaiPrecaution is normally taken early in the design cycle such that the critical wires are routed (sometime hand routed) in the required width to avoid cross-crossing with high frequency digital signals
That was taken into consideration and specifically avoided around all four LM94022 sensors. Yet removing the 0.2n/1n charge cap/s instead placed 3R9k to ground stopped 1st steps sample value from increasing when PWM was active. We did the same for the other sensor also undocumented relative info of our work around though the output can source/sink 7ma. Fear was an input divider may change the analog voltage of the calibrated sensor. Ideally the ground resistor (3R9k) sets the divided voltage above any of the sensor values and wont affect the readings. The cADC switching noise AIN-16 is no longer effecting TSNH step 1 and it was very low level noise below 200mv yet effected the samples.
Oddly the sequencer step may have more to do with switching noise than originally thought. The 1st step would appear to lose TSNH and start drifting but the 2n'd step was always stable during acquisition. We did captured switching spikes coming out of AIN-16 for some reason AIN-16 was spitting spikes onto the channel, perhaps as it lost hold acquisition on the 1st step? Increasing all steps TSNH encoded value could not resolve the issue alone.
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