Other Parts Discussed in Thread: INA282
Puzzled why both REF1,2 connected to ground the A1 outputs are producing very symmetrical and zero crossing wave forms. How is it possible unidirectional current mode produces voltage swings for both current directions in the output signal?
Noticing transient pulses > -400mv below ground and others >20V/V current gain times the shunt resistive and microvolt values. Adversely the amplifier gain and shunt values have no real mathematical perspective when the output appears to persistently over/under shoot during transient pulse production. Likewise the MCU being subjected to negative pulse trash on the ADC input channel often leads to sudden SAR latch up events or clubbing the MCU in the process.
The other odd issue is A1 behavior with an Orion +24vdc fan PWM being amplified by the A1 during idle producing >50mV noise, very odd shaped yet symmetrical transient pules. Unplug the fan or set the speed control 100% duty the A1 idle outputs quiet to <7-10mV noise. Yet the A1 80db@50kHz PSRR(db) rejection (Fig.11) has not stopped 32kHz fan PWM riding on +24v from plaguing the A1's powered via dedicated 3v3 LDO. It would seem datasheet PSRR(db) is not holding true in real world use of the device being laid out identical recommended Fig. 39. It would seem Fig.11 is based on non-valid incorrect testing conditions as there is little to no PSRR(db) in this case!
Both these issues occur with A1 1n load capacitance, 2k series resistance connected to TI designed SAR ADC. What can be done to stop the A1 output from going far below ground as it is doing and why does it not behave as the datasheet states Fig.11 as being factual? Was a multilayer PCB used to evaluate the INA device during laboratory testing of datasheet values, if so why is that not specified in Fig. 39?