JAJSBU6B May 2013 – October 2023 TPS54531
PRODUCTION DATA
The slow-start capacitor determines the minimum amount of time required for the output voltage to reach the nominal programmed value during power up which is useful if a load requires a controlled voltage slew rate. The slow-start capacitor is also used if the output capacitance is very large and requires large amounts of current to quickly charge the capacitor to the output voltage level. The large currents necessary to charge the capacitor can make the TPS54531 device reach the current limit. Excessive current draw from the input power supply can cause the input voltage rail to sag. Limiting the output voltage slew rate solves both of these problems. Use Equation 3 to calculate the value of the slow-start capacitor. For the example circuit, the slow-start time is not too critical because the output capacitor value is 2 × 47 μF which does not require much current to charge to 5 V. The example circuit has the slow-start time set to an arbitrary value of 4 ms which requires a 10-nF capacitor. For the TPS54531 device, ISS is 2 µA and Vref is 0.8 V.