The TPSM8281x starts operation when the rising EN 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. In this mode, the internal high-side and low-side MOSFETs are turned off and the entire internal control circuitry is switched off. The voltage applied at the EN pin of the TPSM8281x is compared to a fixed threshold of 1.1V for a rising voltage.

The enable input threshold for a falling edge is typically 100mV lower than the rising edge threshold. The Precise Enable input provides a user-programmable undervoltage lockout by adding a resistor divider to the input of the EN pin. The Precise Enable input also allows you to drive the pin by a slowly changing voltage and enables the use of an external RC network to achieve a precise power-up delay. See the Achieving a Clean Start-up by Using a DC/DC Converter with a Precise Enable-pin Threshold analog design journal for more details.