SLRS066D January 2014 – March 2016 TPL7407L
The COM pin is the power supply pin of this device to power the gate drive circuitry. This ensures full drive potential with any GPIO above 1.5 V. The gate drive circuitry is based on low voltage CMOS transistors that can only handle a max gate voltage of 7 V. An integrated LDO reduces the COM voltage of 8.5 V to 40 V to a regulated voltage of 7 V. Though 8.5 V minimum is recommended for Vcom, the part will still function with a reduced COM voltage that has a reduced gate drive voltage and a resulting higher Rdson.
The COM pin must be limited to below 0.5 V/μsTo prevent overvoltage on the internal LDO output due to a line transient on the COM pin. Faster slew-rate (or hot-plug) may cause damage to the internal gate driving circuitry due to the LDO's inability to clamp a fast input transient fast enough. Since most modern power supplies are loaded by capacitors > 10 μF, this should not be of any concern. It is recommended to use a bypass capacitor that will limit the slew rate to below 0.5 V/μs.
Figure 11 is a great example where repetitive slew rates may occur on the Vcom pin. 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 and resistance, this can be very rapid.
In summary, whenever the COM pin may experience a slew rate greater than 0.5 V/µs a capacitor must be added to limit the slew to < 0.5 V/µs.