Probing RSENSE in POWERSTEP01

[darshangad]

We are designing an independent current monitoring circuit for a motor driven by the powerSTEP01. We are using a 0.1 ohm low-side sense resistor (RSENSE).

When probing the voltage across this sense resistor with an oscilloscope, we are observing a distinct PWM waveform where the negative voltage pulses have almost the exact same amplitude as the positive voltage pulses (flipping symmetrically below ground, e.g., +0.5V and -0.5V. )

Screenshot: RSENSE voltage generated across 0.1ohm when motor is rotating in current mode 

 

Before I modify my external analog front-end (currently using an RC filter, a clamp diode and an op-amp) to handle these negative swings, I want to double-check my findings.

1. Is this symmetrical negative voltage pulse an expected physical phenomenon of the powerSTEP01 H-bridge operating in Fast Decay / synchronous rectification mode?
2. Or am I likely dealing with an oscilloscope probing/grounding issue, such as ground bounce or parasitic inductance artifacts?

Any insights into whether this is true back-EMF/recirculation current or just measurement noise would be greatly appreciated!

Thanks in advance.

[AScha.3]

I dont know  your circuit and where is the scope probe….

but just guessing from the signal on the DSO : looks very clean, good ground of scope probe etc. , 

so the partial almost symmetrical pos./negative voltage shows just the ( pos. )current to a coil and its back EMF , current flowing “out” of the coil, (neg.) as the current/mag.field dissipates.

Perfect shown on scope.