Could you see any problems with just connecting those lines straight to ground? I tried that and while things do indeed get hot they are still within the safe temps outlined in the datasheet (130 max - 75 as a "normal" temp). It pulls about 3-4.5A as compared to 2-3.5A.
What does changing Vref actually do? I know it varies how many amps are pulled but what is it actually adjusting? is it like PWM or something?
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Connecting them directly to ground would be a very bad thing to do.
The current limiting counts on the voltage drop across the resistors. It works like this:
The motor current goes through the L298 out pin 1&15 through the resistors to ground. From Ohms law, the voltage across a resistor is equal to the current times the resistance(ie the resistor converts the current into a voltage). For example, with a 0.5 ohm resistor, 1 amp would give 0.5 volts, 2 amps would give 1 volt, etc. Inside the L297 is a voltage comparator that compares the voltage across the resistor with the reference voltage. When the voltage across the resistor goes higher than the reference voltage, the L297 shuts off the L298 for a fixed amount of time. With a direct connection to ground instead of a resistor, the only resistance would be that of the wiring and connections, and it would take a very high current to generate a voltage equal to the reference voltage.