This show a classic HEXFET half-bridge driver. IR2103 takes 3.3V logic in form of PWM and convert it into levels that can drive the HEXFET’s. This is called a Gate Driver. It’s purpose is to deliver signals on correct voltage levels to drive the HEXFET’s. A typical minimum for a gate driver is 10ich Volt. The two HEXFET’s shown are IRF7862 capable of 30V and 17A @ 70 degrees. My target is 12-24V/10A, so this should be sufficient. The pulse drain is 170A and temperature up to 150 degrees.
The nice thing about these SO8 based HEXFET’s is that many of the use the same pin layout. I know of far more capable one’s, but their cost was much higher.
I am a little unsure about HIN/LIN on IR2103. I have a preference of wanting to program everything, but these can be connected to depend on 4 PWM inputs rather than 8.
R1 is the current shunt. This must be feed to an op amp and adjusted a bit. The diagram say 0.005 Ohm, but I was more interested in the correct footprint than the actual value. Measuring currents like this is not straight forward, so I need to experiment a bit with this. In a 3-phase motor we need 2 shunts, but 3 is preferred. In a 2-phase stepper we only need 1 for torque calculations.