VNH5019 pin question and control question

Why are there MxINA (clockwise input) and MxINB (CCW input) instead of just a single direction pin?

I plan on using this board to control motors that transfer wire from one spool to another (like a cassette player, but the spools are different sizes). The reason I need two motors is to maintain a constant tension in the wire (via closed loop control w/ tension sensor). Which option do you think would be better:

  1. Drive motor_1 CW at fixed speed and have motor_2 CCW controlled in “drive-coast operation” to maintain tension?

  2. Drive motor_1 CW at fixed speed and have motor_2 CCW controlled in “drive-brake operation” to maintain tension?

User guide: “Note that it is possible to get by with even fewer connections if you use pulse-width modulation (PWM) on the MxINA and MxINB pins directly while holding the MxPWM pin high (e.g. by connecting it directly to VDD). This approach also results in a different kind of motor-driving: supplying the PWM signal to the MxINA/B pins directly results in drive-brake operation (outputs drive during the high portion of the PWM and are shorted together during the low portion), while supplying the PWM signal to the MxPWM pin results in drive-coast operation (outputs alternate between driving and high-impedance).”

I am not completely clear on how the drive-brake operation works.

It is a trade off between control and interfacing ease.

Generally you get better performance with drive-brake operation. In this case, though, the rise and fall times of when switching the INx pins is 250 times longer than when switching PWM, so you have to have a significantly lower PWM frequency when doing drive-brake operation. Lowering the PWM frequency brings it into the audible range and will make your setup louder.

When the h-bridge is braking, both motor wires are shorted to the same voltage. Shorting them to ground is generally preferred. When the h-bridge is coasting all of the FETs are off (current still circulates through the FET body diodes). You can refer to the truth table in the datasheet on page 15 for details on how you would achieve the operation you want.

- Ryan