Current sensing noise consideration in FoC capable BLDC Motor driver

[satyamfifa]

Hey Guys,

I am designing a 48V, 30A continuous current FoC capable BLDC motor driver. I want to do in-line current and voltage sensing in all three phases plus total current sensing. For this I was to use shunt resistor about 0.001 each connected to INA240 current sense amplifier which is connected ADS7947 (12 bits 2MSPS) ADCs which has SPI interface, each ADC has two channels therefore I am thinking of using one channel for measuring phase current and other for phase voltage. I am thinking of placing one shunt resistor, amplifier and ADC close together for each phase.

However, the thing I am really considering now is the impact noise generated by MOSFETs switching high current on current sensing circuit and how can it be minimized. I am considering using separate ground planes for the sensing circuit, I have been doing quite some research on separating ground planes and I have heard argument both for and against doing so, and because I am measuring frequencies below 20 kHz, I am thinking this could be good idea. I understand that ADCs and Amplifiers referencing should be tightly coupled together since any noise / offset with affects them both will be cancelled out.

Another design decision that I am not really sure about is weather to power the analog circuit from 3.3V directly from the logic board, to power it with 5V requiring me to add a LDO which is sourced from 48 V input.

Finally, I am also concerned about the signal integrity of the SPI signals if the ADCs are placed close to amplifiers which mean they might be placed further away from the logic board. I assume that SPI clock frequency will be a typical of 34 MHz.

I think the right component placement will be key to achieving the most optimal design. I would really appreciate any suggestions, tips, possible solutions, considerations etc.

Kind Regards,
Sparsh

[Benta]

The most ambitious and problematic point in your post is using 1 m\$\Omega\$ resistors for current sensing.

[jonathan_nadar]

You can refer to this document from TI.