The CMOS input pin must be asserted to the desired voltage for operation. An internal pullup resistor is not provided on the PD pin so that off-state quiescent current can be minimized. For applications simply requiring the device to be powered on when the supplies are present, tie the PD pin to the positive supply voltage.

The disable operation is referenced from the negative supply, normally ground. For split-supply operation, with the negative supply below ground, a disable control voltage below ground is required to turn the THS4551 off. To assure an off state condition, the disable control pin must be below a voltage within 0.55 V of the negative supply.

For single-supply operation, a minimum of 1.15 V above the negative supply (ground in this case) is required to assure on operation. This logic threshold range allows direct operation from a 1.8-V supply logic when the THS4551 operates with a single positive supply and ground.