Other Parts Discussed in Thread: EK-TM4C1294XL, INA282, INA240, , LM4120
EK-TM4C1294XL
Circuit & configuration : 3 single ended ADC analog inputs current monitors signal jots 200mv below ground in a cyclic loop. Same 3 amplified resistive gain reduced signals also feed 3 onboard digital comparators respectively the outputs feed 3 PWM0-M0nFault input trigger pins. Analog Digital comparator thresholds are set 14.4 amps maximum and have +VREFA rail as the voltage source for internal VREF resistor bridge. Actual detected digital running current (6.7-8.6 amps) roughly 5.8 amps below the digital comparators maximum trip point 3.6 amps and below the minimum trip point 12.2 amps where 13.3 amps ideal. But.....
Issue: Random PWM faulting is occurring when respectively no over current threat exists.
1st remedy: Changed R41 (0R0) XLTM4C launch pad to R41=10kR0 to isolate and limit +VREFA 300na. Also added 0.01uf ceramic to ground at the +VREFA input pin.
Results: Far less random comparator trips resulted yet did not completely arrest the phantom faulting condition.
2nd remedy: Add 1nf capacitors directly across low side INA282 current monitor shunt resistors.
Results: Even less random analog comparator trips occurred yet did not completely arrest phantom faulting.
Suspecting comparator inputs jotting below ground has some effect on the internal +VREFA that reduces the minim trip threshold by 200mv or more but unclear as to why.
Question:
1. Please elaborate why random comparator trips occur when GNDA is at 0v0 potential or how signal below ground (single ended ADC) violates datasheet specifications?
2. Does signal jotting 200mv below ground cause TM4C errata when the INA282 current monitor can senses bipolar CMM up to -14v and GNDA is 0v0 potential?
3. INA240 claims -4v CMM and likely could reduce GNDA artifact and some PWM noise (dv/dt) input to analog comparators.
Any thoughts or suggestions how GNDA in production runs should be handled or how to test rig the XL launch pad to halt the phantom?
CH1: FET turns off then back on. CH2: INA282 monitors the current rise.