- Tue Mar 13, 2018 11:46 am
#198651
Hi, can anyone help me understand how the A3967 controls the current through its internal H-bridge? Here's what I think I know from poking around the EasyDriver with a scope and looking through the A3967 datasheet--please correct me if I'm wrong:
- The H-bridge is pulsed at 32kHz
- The output current is proportional to the duty cycle
- The A3967 measures the voltage across the current sensing resistor, compares it with the DAC output representing the target voltage, and adjusts the duty cycle accordingly.
- why isn't there insane amounts of inductive kickback at the output pins due to all that switching? I expected to see peaks at a diode drop above the load supply and/or below ground.
- the signals at the sense resistor pins 8 and 17 just look like noisy square waves. Are they being continuously compared with their corresponding DAC output, or being sampled at some point?
- I originally assumed that the inductance of the motor coils, together with the sense resistor, would form a low pass filter and smooth out the current. The fact that I'm seeing square waves at the sense resistor pins implies that's not true, right?