SNVSC41 November 2023 LMR36500
PRODMIX
The voltage at the EN/UVLO pin controls the start-up voltage and shutdown voltage of the LMR36500. There are three distinct modes set by the EN/UVLO pin; shut-down, standby and active. As long as the EN/UVLO pin voltage is less than VEN-WAKE the device is in shutdown mode. During shutdown mode, the input current drawn by the device typically is 0.5 µA (VIN = 13.5 V). The internal LDO regulator is not operational. When the voltage at the EN/UVLO pin is greater than VEN-WAKE but less than VEN-VOUT the device enters the standby mode. In standby mode, the internal LDO is enabled. As the EN/UVLO pin voltage increases above VEN-VOUT, the device enters active mode starting the feedback resistor detection. After feedback detect is completed, soft-start functionality is released to slowly increases the output voltage and switching starts. To stop switching and enter standby mode the EN/UVLO pin must fall below (VEN-VOUT – VEN-HYST). Any further decrease in the EN/UVLO pin voltage below VEN-WAKE puts the device in shutdown. The various EN/UVLO threshold parameters and their values are listed in Section 6.5. See Section 7.3.6 for information about feedback resistor selection. Figure 7-1 shows the precision enable behavior.
External precision undervoltage lockout can be implemented with this functionality as shown in Figure 7-2. See Section 8.2.2.9 for component selection.
The high-voltage compliant EN/UVLO pin can be connected directly to the VIN input pin if external precision control is not needed. The EN/UVLO pin must not be allowed to float. The various EN threshold parameters are listed in the Section 6.5. Figure 7-1 shows the precision enable behavior. After EN/UVLO goes above VEN-VOUT with a delay of about 1 ms, the output voltage begins to rise with a soft-start and reaches close to the final value in about 2.58 ms (tss). After a delay of about 2 ms (tPGOOD_ACT), the PGOOD flag goes high. During startup, the device is not allowed to enter FPWM mode until the soft-start time has elapsed. Check Section 8.2.2.9 for component selection. Refer to Figure 7-3 for a typical start-up waveform.