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 LM5146 is to connect EN/UVLO directly to VIN. This allows self start-up of the LM5146 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 LM5146 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 LM5146. The LM5146 operates in standby mode when the EN/UVLO voltage is between the hard shutdown and precision enable (standby) thresholds.