The TPS2585x-Q1 is in active mode when V_EN is above the precision enable threshold, V_SENSE is above its respective UVLO levels and a valid detection has been made on the CC lines. The simplest way to enable the TPS2585x-Q1 is to connect the EN pin to SENSE pin. This connection allows self startup when the input voltage is in the operating range (5.5 V to 26 V) and a UFP detection is made.

In active mode, the TPS25850-Q1 buck regulator does not operate unless Rd is inserted, the TPS25851-Q1 and TPS25852-Q1 buck regulator operates even though Rd is not inserted. Then the buck regulator operates with Forced Pulse Width Modulation (FPWM), also referred to as Forced Continuous Conduction Mode (FCCM). This action ensures the buck regulator switching frequency remains constant under all load conditions. FPWM operation provides low output voltage ripple, tight output voltage regulation, and constant switching frequency. Built-in spread-spectrum modulation aids in distributing spectral energy across a narrow band around the switching frequency programmed by the FREQ/SYNC pin. Under light load conditions the inductor current is allowed to go negative. A negative current limit of I_L-NEG-LS is imposed to prevent damage to the regulator's low side FET. During operation, the TPS2585x-Q1 synchronizes to any valid clock signal on the FREQ/SYNC input.