When the enable pin is low, the device enters shutdown mode and does not regulate the output voltage. Normally, an external resistor divider from V_IN to GND is used to feed EN.

Connection of the Enable pin directly to V_IN is possible when V_IN is below the Recommended Operating level of 7V; if a higher voltage level is to be provided to the Enable pin, then a simple voltage divider can be applied, refer to Equation 2 for resistor sizing guidance at the desired turn-on voltage.

Similarly, a V_IN(falling) voltage can also be calculated using Equation 3. The V_IN(rising) and V_IN(falling) can be thought of as configurable UVLO (under voltage-lockout) thresholds.

While the TPS7H1121 will turn-on at a voltage of V_EN of 0.6V (typ), it is recommended that the final value is above 0.8V. This is to ensure appropriate margin above the enable threshold during normal operation to prevent SEFIs during exposure to heavy ions. This recommendation is achieved by satisfying Equation 4.

Alternatively, the EN pin can be driven directly from a micro-controller or FPGA. The low voltage threshold of the enable pin aids in support of 1.1V, 1.8V, 2.5V, and 3.3V logic levels. Similarly a final V_EN above 0.8V for direct logic level driving is recommended (this is typically easily achieved with standard logic levels).