The EN/UVLO input supports adjustable input undervoltage lockout (UVLO) with hysteresis programmed by the resistor values for application specific power-up and power-down requirements. EN/UVLO connects to a comparator-based input referenced to a 1.2-V bandgap voltage. An external logic signal can be used to drive the EN/UVLO input to toggle the output ON and OFF and for system sequencing or protection. The simplest way to enable the operation of the LM5145-Q1 is to connect EN/UVLO directly to VIN. This allows self start-up of the LM5145-Q1 when V_CC is within its valid operating range. However, many applications benefit from using a resistor divider R_UV1 and R_UV2 as shown in Figure 8-3 to establish a precision UVLO level.

Use Equation 1 and Equation 2 to calculate the UVLO resistors given the required input turn-on and turn-off voltages.

Equation 1.

Equation 2.

The LM5145-Q1 enters a low I_Q shutdown mode when EN/UVLO is pulled below approximately 0.4 V. The internal LDO regulator powers off and the internal bias supply rail collapses, shutting down the bias currents of the LM5145-Q1. The LM5145-Q1 operates in standby mode when the EN/UVLO voltage is between the hard shutdown and precision enable (standby) thresholds.