Does TB6612FNG require additional circuit to control motor and why
This additional circuit is a Reverse Polarity Protection using P-Channel Enhanced MOSFET.
Do we need this circuit ? Yes I think we need this as a protection circuit, It depends on use case.
The VMOT supplies the input power from the source i.e. battery or bench power supply.
The components used are P-Channel MOSFET, Pull-Down Resistor, Zener Diode and few Decoupling Capacitors.
The main intention of this circuit is to protect the IC TB6612FNG from reverse voltages.
How this circuit works:

If the voltage between &quot;Gate-to-Source&quot; of P-Channel MOSFET is negative the P-Channel MOSFET is turned ON
If the voltage between &quot;Gate-to-Source&quot; of P-Channel MOSFET is positive the P-Channel MOSFET is turned OFF

Power loss in this type of circuit is less compared to using a diode or diode bridge.
We have zener diode and resistor in the circuit to protect against exceeding gate to source voltage, so as to protect the MOSFET.
Decoupling capacitors helps to isolate noise, it must be placed close to the IC TB6612FNG pins.