None of the required C_OUT output capacitance is contained within the module. A minimum value ranging from 330 μF for 6 V_OUT to 660 μF for 1.2-V_OUT applications is required based on the values of internal compensation in the error amplifier. These minimum values can be decreased if the effective capacitor ESR is higher than 15 mΩ.

A low-ESR (15 mΩ) tantalum, organic semiconductor or specialty polymer capacitor types in parallel with a 47-nF X7R ceramic capacitor for high-frequency noise reduction is recommended for obtaining lowest ripple. The output capacitor C_OUT can consist of several capacitors in parallel placed in close proximity to the module. The output voltage ripple of the module depends on the equivalent series resistance (ESR) of the capacitor bank, and can be calculated by multiplying the ripple current of the module by the effective impedance of your chosen output capacitors. Electrolytic capacitors will have large ESR and lead to larger output ripple than ceramic or polymer types. For this reason, a combination of ceramic and polymer capacitors is recommended for low output ripple performance.

The output capacitor assembly must also meet the worst case ripple current rating of Δi_L. Loop response verification is also valuable to confirm closed loop behavior.

For applications with dynamic load steps; Equation 10 provides a good first pass approximation of C_OUT for load transient requirements.

Equation 10.

For 12 V_IN, 3.3 V_OUT, a transient voltage of 5% of V_OUT = 0.165 V (ΔV_OUT), a 9-A load step (I_STEP), an output capacitor effective ESR of 3 mΩ, and a switching frequency of 350 kHz (f_SW):

Equation 11.

One recommended output capacitor combination is two 330-μF, 15-mΩ ESR tantalum polymer capacitors connected in parallel with a 47-µF 6.3-V X5R ceramic. This combination provides excellent performance that can exceed the requirements of certain applications. Additionally some small 47-nF ceramic capacitors can be used for high-frequency EMI suppression.