The enable (EN) pin is active high and is compatible with standard digital-signaling levels. V_EN below 0.4V turns the regulator off and V_EN above 1.1V turns the regulator on. Unlike many regulators, the enable circuitry has hysteresis and deglitching for use with relatively slowly ramping analog signals. This configuration allows the TPS74901 to be enabled by connecting the output of another supply to the EN pin. The enable circuitry typically has 50mV of hysteresis and a deglitch circuit to help avoid ON-OFF cycling because of small glitches in the V_EN signal.

The enable threshold is typically 0.8V and varies with temperature and process variations. Temperature variation is approximately –1mV/°C; process variation accounts for most of the rest of the variation to the 0.4V and 1.1V limits. If precise turn-on timing is required, a fast rise-time signal must be used to enable the TPS74901.

If not used, EN can be connected to either IN or BIAS. If EN is connected to IN, then connect EN as close as possible to the largest capacitance on the input to prevent voltage droops on that line from triggering the enable circuit.

The TPS749 has an internal active pulldown circuit that connects the output to GND through an 833Ω resistor when the device is disabled. This resistor discharges the output with a time constant of:

$\tau \text{ = }\left(\frac{833 \times R_L}{833+ R_L}\right)\text{ × }{C}_{OUT}$