Other Parts Discussed in Thread: DRV421, DRV425
I'm working with the DRV421 evaluation module, attempting to measure a relatively low current of ~50 mA. I'm able to read the signal, but there is also significant noise in the system. I have an overall gain of approximately 1, so the 50 mA current results in a 50 mV shift in the output signal. Unfortunately there is also about 50 mV of periodic noise on the signal, so the S/N ratio is rather poor.
I have read through several other forum posts for this module and I'm aware of the 8 uT offset, and have also developed magnetic shielding for the toroid using a triple layer of MuMetal. I have also built a minimal interface board that brings the output signal into coax within a few mm of the connector to the eval board while still inside the magnetic shielding.
Following is an image of my core and compensation coil inside the magnetic shield. When fully assembled the core and coil are axially centered within the shielding material.
Since the current I'm trying to measure is small I am using a smaller number (~350) turns on the compensation coil to increase the gain.
Is it typical to see so much noise from this sensor, or is this a result of a low number of turns that might be marginal on overall inductance?
Can you suggest any methods for reducing noise on the signal?