The voltage applied at the Enable pin of the TPS6281x-Q1 is compared to a fixed threshold of 1.1 V for a rising voltage. This allows to drive the pin by a slowly changing voltage and enables the use of an external RC network to achieve a power-up delay.
The Precise Enable input provides a user-programmable undervoltage lockout by adding a resistor divider to the input of the Enable pin.
The enable input threshold for a falling edge is typically 100 mV lower than the rising edge threshold. The TPS6281x-Q1 starts operation when the rising threshold is exceeded. For proper operation, the EN pin must be terminated and must not be left floating. Pulling the EN pin low forces the device into shutdown, with a shutdown current of typically 1 μA. In this mode, the internal high-side and low-side MOSFETs are turned off and the entire internal control circuitry is switched off.