I am using part number OPA2863RUNR as a buffer amplifier. This amp features a power-down pin. The amplifier IC package is powered with 5VDC.
I am observing that when the power-down pin is above 3.9VDC the output buffer follows the 4.096VDC reference as expected with a 350-Ohm load, and a short circuit current of 64mA.
However, when the power-down pin is anywhere between 0.00VDC and 3.90VDC with respect to ground, the output does not shut off but remains at 1.864V with a 350-Ohm load, and with a short circuit current of 18mA.
Why is a power-down pin voltage below the turn-on threshold not causing a Hi-Z condition on the output?