JAJSIR5C October 2019 – October 2023 TPS65313-Q1
PRODUCTION DATA
The minimum output capacitance for each regulator is 25 µF and the maximum output capacitance is defined as 100 µF. X7R-type, low-ESR ceramic capacitors are recommended. The minimum and maximum capacitance values specified are the effective capacitance values after considering all the tolerances, voltage derating, and aging effects. Therefore, users must use the value that is higher than the specified value to accommodate for these variations. Select the output capacitor value to be 1.5 times the minimum required capacitance value. The output capacitance range allows users to optimize the output voltage ripple and load transient performance according to their application conditions. Selecting the output capacitance value within the specified range is important to meet the stability requirements of the regulators. Stability performance must be measured on the application board to make sure that regulators are stable for the selected output capacitor.
Use Equation 6 to calculate the output capacitance (COUT) value based on the load transient requirements.
where
Use Equation 7 to calculate the peak-to-peak output voltage ripple.
where
For this example, the BUCK1 voltage is 3.3 V with a 2% change in the output voltage for a load step from 0 A to 2 A. The resulting value of the BUCK1 output capacitance is approximately 28 µF. Considering the capacitor tolerances, derating, and aging effects, two 22-µF, 10-V rating, X7R-type capacitors (GCM31CR71A226KE02 from Murata) are used.
For this example, the calculated BUCK1 output voltage ripple is approximately 11 mVPP for a typical 44-µF capacitor with 3-mΩ effective ESR, 1-nH ESL, 18-V input voltage, 3.3-V output voltage, 3-A maximum load current, and an inductor ripple current that is approximately 20% of the maximum load current.
For this example, the BUCK2 voltage is 1.8 V with a 2 % change in the output voltage for a load step from 0 A to 1 A. The resulting value of the BUCK2 output capacitance is approximately 25 µF. Considering the capacitor tolerances, derating, and aging effects, two 22-µF, 10-V rating, X7R-type capacitors (GCM31CR71A226KE02 from Murata) are used.
For this example, the calculated BUCK2 output voltage ripple is approximately 5 mVPP for a typical 44-µF capacitor with 3-mΩ effective ESR, 1-nH ESL, 3.3-V input voltage, 1.8-V output voltage , 1-µH inductor, 2-A maximum load current, and an inductor ripple current that is approximately 20% of the maximum load current.