SLVSGP3A May 2023 – February 2024 TPS54KB20
PRODUCTION DATA
When the EN pin voltage rises above the enable threshold voltage (VEN(R)) and VIN rises above the VIN UVLO rising threshold, the device enters the internal power-up sequence. The EN to start of switching delay is specified in the STARTUP section of the Electrical Characterisitcs table.
The EN pin has an internal filter to avoid unexpected ON or OFF due to small glitches. The time constant of this RC filter is 2µs. For example, when applying 3.3V voltage source on the EN pin that jumps from 0V to 3.3V with an excellent rising edge, the internal EN signal reaches 2.1V after 2µs, which is 63.2% of applied 3.3V voltage level.
An internal pulldown resistor is implemented between the EN pin and AGND pin. With this pulldown resistor, floating the EN pin before start-up keeps the device in the disabled state. A resistor divider to the EN pin can be used to increase the input voltage the device begins the start-up sequence. The internal pulldown resistor must be accounted for when using an external resistor divider. To reduce impact to the EN rising and falling threshold, this internal pulldown resistor is 1MΩ. During nominal operation when the power stage switches, this large internal pulldown resistor can not have enough noise immunity to hold EN pin low for the device to enter the disabled state.
The recommended operating condition for the EN pin is a maximum of 5.5V. Do not connect the EN pin to the VIN pin directly if VIN can exceed 5.5V.