7.3.3 Soft Start and Pre-Biased Soft Start

The TPS566235 has an internal 1.0 ms soft-start time. Soft start can prevent the overshoot of output voltage during start up. When the EN pin becomes high, internal soft-start function begins ramping up the reference voltage to the PWM comparator.

The TPS566235 can prevent current from being pulled from the output during startup if the output is pre-biased. The device disables the switching of both the high-side and low-side FETs until the soft-start commands a voltage higher than the pre-bias level (internal soft start becomes greater than feedback voltage V_FB). Then, the controller start the first high side FET gate driver pulses. This scheme prevents the initial sinking of the pre-bias output, and ensure that the output voltage starts and ramps up into regulation and the control loop is given time to transition from pre-biased start-up to normal mode operation.