9.3.3 Soft Start

The TPS8269xSIP has an internal soft-start circuit that limits the inrush current during start-up. This limits input voltage drops when a battery or a high-impedance power source is connected to the input of the MicroSIP^TM converter.

The soft-start system progressively increases the switching on-time from a minimum pulse-width of 35ns as a function of the output voltage. This mode of operation continues for approximately 100μs after enable. Should the output voltage not have reached its target value by that time, such as in the case of heavy load, the soft-start transitions to a second mode of operation.

If the output voltage has raised above 0.5V (approximately), the converter increases the input current limit thereby enabling the power supply to come-up properly. The start-up time mainly depends on the capacitance present at the output node and load current.