I want to use an AD8418 (http://www.analog.com/media/en/technical-documentation/data-sheets/AD8418.pdf) together with the ADC of the uC to measure the current of a BLDC motor for two phases, that is used for field oriented control. As a driver I use a DRV8313 (http://www.ti.com/lit/ds/symlink/drv8313.pdf) which allows to connect the shunt resistor to the low-side mosfet. My question is now where I should put my shunt resistors to measure the currents:
1.) Directly to the phases of the BLDC motor. This is found in the application note of the AD8418.
2.) Put the shunt resistors to the low side mosfets.
When I put the shunts to the low side mosfets, I need to measure the current only when the low-side mosfet is active. For that, I need center-aligned PWM to trigger the ADC in the right moment. Is this also needed when I put the shunt resistors to the BLDC phases and if yes, when needs the current to be measured? Are there any advantages with method 1.)? The actual PWM signal will be around 25kHz, where the CMRR is about 80dB, that should be still enough.
Here is also a schematic of how I planned to do it with the method 1.)