SNVSB79B November 2018 – May 2020 LM25180
The precision EN/UVLO input supports adjustable input undervoltage lockout (UVLO) with hysteresis for application specific power-up and power-down requirements. EN/UVLO connects to a comparator with a 1.5-V reference voltage and 50-mV hysteresis. An external logic signal can be used to drive the EN/UVLO input to toggle the output on and off for system sequencing or protection. The simplest way to enable the LM25180 is to connect EN/UVLO directly to VIN. This allows the LM25180 to start up when VIN is within its valid operating range. However, many applications benefit from using a resistor divider RUV1 and RUV2 as shown in Figure 21 to establish a precision UVLO level.
Use Equation 10 and Equation 11 to calculate the input UVLO voltages turn-on and turn-off voltages, respectively, where VUV-RISING and VUV-FALLING are the UVLO comparator thresholds and IUV-HYST is the hysteresis current.
The LM25180 also provides a low-IQ shutdown mode when the EN/UVLO voltage is pulled below a base-emitter voltage drop (approximately 0.6 V at room temperature). If the EN/UVLO voltage is below this hard shutdown threshold, the internal LDO regulator powers off, and the internal bias-supply rail collapses, shutting down the bias currents of the LM25180. The LM25180 operates in standby mode when the EN/UVLO voltage is between the hard shutdown and precision-enable thresholds.