The voltage on the EN pin controls the ON or OFF operation of the LMR38020. A voltage below 0.95 V shuts the device down, while a voltage above 1.4 V is required to start the converter. The EN pin is an input and cannot be left open or floating. The simplest way to enable the operation of the LMR38020 is to connect the EN to VIN. This allows self-start-up of the LMR38020 when V_IN is within the operating range.

Many applications benefit from the employment of an enable divider R_ENT and R_ENB (Figure 8-3) to establish a precision system UVLO level for the converter. System UVLO can be used for supplies operating from utility power as well as battery power. System UVLO can be used for sequencing, making sure the user has reliable operation or supply protection, such as a battery discharge level. An external logic signal can also be used to drive EN input for system sequencing and protection. Note that the EN pin voltage must never be higher than V_IN + 0.3 V.

Figure 8-3 System UVLO by Enable Divider