Zener diode in stepper motor driver with TPL7407L
9.2.2.1 Design Requirements - [...] Whenever a Zener diode is used between Vcom and the motor supply, the Vcom pin will slew from the coil supply to a voltage that is the sum of the Zener voltage and the coil supply when there is a flyback event. Depending on the coil inductance &amp; resistance, this can be very rapid. Whenever the COM pin may experience a slew rate greater than 0.5 V/ μ s a capacitor must be added to limit the slew to &lt; 0.5 V/ μ s. See Power Supply Recommendations for further explanation.


So in this particular case you should either:


Add a zener diode from motor supply to V(COM) and forget the V(SUP) at the V(COM) node.
Short both nodes V(COM) to motor supply.


The advantage for 1. is that the energy stored in the motor coils is being broken down more quickly and the stepper response will be 'snappier'. Notice that the motor supply increased with the zener voltage must not exceed 42V (absolute maximum, so you want to be well below that).