I'm trying to build a brushless dc motor driver, which provides the possibility to measure the currents on all three phases of the motor independently.
The driver IC that I'm using (DRV8313) has three pins broken out for low-side current sensing using a shunt resistor.
I'm familiar with the basic concept of a shunt resistor, but I find it hard to select a suitable amplifier (opamp,…) and design the needed circuit around it.
Some information about my project: The maximum current is 2.5A, but most of the time it will not exceed 1A. The ADC I'm going to use has a 3.3V reference voltage. Thus, using an 0.1Ohm resistor would result in a voltage drop of 250mV, which had to be amplified by about 13V/V for the ADC.
My question is, how exactly do I design a low-side current sensing circuit? Which criteria does the opamp have to meet?
Looking forward to any kind of help. 🙂
Best Answer
If you want independent monitoring of all three sense resistors then use an op-amp like the AD8608 quad op-amp - it has rail-to-rail capabilities and use three of the op-amps as non-inverting amplifiers like this: -
Gain is Rf/Rg + 1. I would also put an RC low pass filter in line with the non-inverting input - probably initially try 10k and 10nF. This also acts to protect the op-amp inputs should there be ground bounce.