Occasionally applications do not need all the comparators in a dual or quad package. The unused channels must be connected in a way that is safe for the unused comparator and doesn’t affect the used comparators. The best connection method puts the comparator into the normal operation range and no inputs are connected directly to low impedance nodes. The output of the comparator must be left open and not connected.

Figure 9-1 Best Connections Practices for Single and Dual Supplies

Increasing the input resistor to 10MΩ maintains linear operation as the input bias current (I_b), which flows out of the input pin towards ground, raises the non-inverting input voltage beyond the input offset voltage range. V_OL Full V_ID is better suited for lower voltage applications as there is no reason to apply a large input voltage difference even though the comparator allows these large voltages. The V_OL (I_IB Biased) method uses the input bias current to raise the voltage on the inverting input. If used, place the 10MΩ resistor close to the inverting input pin to reduce noise pickup. No inputs can be connected directly to low impedance nodes such as ground, V_CC or V_EE. V_OH alternatives are also acceptable; just swap the input pins.

The next set of connections in Figure 9-2 is not recommended, but these configurations are not considered harmful methods of terminating unused channels. The V_OH alternatives that swap the inputs are also not recommended methods of terminating unused channels.

Figure 9-2 Less Than Acceptable Connection Practices for Single and Dual Supplies

The last set of connections, shown in Figure 9-3, demonstrates improper setups that can cause output noise chatter or device damage if the GND pin were to ever become positive relative to the input pin.

Figure 9-3 Potentially Harmful Connection Practices for Single and Dual Supplies