The device is in low power mode if the IN terminal voltage is less than VUVLO, so the part is considered dead and all the terminals are high impedance. Once the IN voltage rises above the VUVLO threshold, the IC enters sleep mode or active mode, depending on the EN/UVLO voltage.

The voltage on the EN/UVLO pin controls the ON/OFF operation of the TPS2585x-Q1. An EN/UVLO pin voltage higher than V_EN/UVLO-H is required to start the internal regulator and begin monitoring the CCn lines for a valid Type-C connection. The internal USB monitoring circuitry is on when V_IN is within the operation range and the EN/UVLO threshold is cleared. For TPS25850-Q1, the buck regulator and the USB ports load switch remains OFF until a valid Type-C detection has been made. For TPS25851-Q1 and TPS25852-Q1, the buck regulator starts to operate, however, the USB ports load switch remains OFF until a valid Type-C detection has been made. This feature ensures the cold socket (0 V) USB Type-C V_BUS requirement is met.

The EN/UVLO pin is an input and cannot be left open or floating. The simplest way to enable the operation of the TPS2585x-Q1 is to connect EN to SENSE. This connection allows self-startup of the TPS2585x-Q1 when V_IN is within the operation range. Note that you cannot connect the EN to IN pin directly for self-startup.

Many applications benefit from the employment of enable dividers R_ENT and R_ENB to establish a precision system UVLO level for the TPS2585x-Q1 shown in Figure 10-1. The system UVLO can be used for sequencing, ensuring reliable operation, or supply protection, such as a battery discharge level. To ensure the USB port V_BUS is within the 5-V operating range as required for USB compliance (for the latest USB specifications and requirements, refer to USB.org), TI suggests that the R_ENT and R_ENB resistors be chosen such that the TPS2585x-Q1 enables when V_IN is approximately 6 V. Considering the dropout voltage of the buck regulator and IR losses in the system, 6 V provides adequate margin to maintain V_BUS within USB specifications. If system requirements, such as a warm crank (start) automotive scenario, require operation with V_IN < 6 V, the values of R_ENT and R_ENB can be calculated assuming a lower V_IN. An external logic signal can also be used to drive the EN/UVLO input when a microcontroller is present and it is desirable to enable or disable the USB port remotely for other reasons.

Figure 10-1 System UVLO by Enable Divider

UVLO configuration using external resistors is governed by the following equations:

Equation 1.

Equation 2.

For example:

V_IN(ON) = 6 V

R_ENT = 20 kΩ

R_ENB = 5 kΩ

Therefore, V_IN(OFF) = 5.5 V