8.2.2.2 Input Capacitor (C_IN)

Low ESR multi-layer ceramic capacitors (MLCC) are recommended for the input capacitor of the LMZ21701. Using a ≥ 10 µF ceramic input capacitor in ≥ 0805 (2012 metric) case size with 25-V rating typically provides sufficient VIN bypass. Use of multiple capacitors can also be considered. Ceramic capacitors with X5R and X7R temperature characteristics are recommended. These provide an optimal balance between small size, cost, reliability, and performance for applications with limited space. The DC voltage bias characteristics of the capacitors must be considered when selecting the DC voltage rating and case size of these components. The effective capacitance of an MLCC is typically reduced by the DC voltage bias applied across its terminals. Selecting a part with larger capacitance, larger case size, or higher voltage rating can compensate for the capacitance loss due to the DC voltage bias effect. For example, a 10-µF, X7R, 25-V rated capacitor used under 12-V DC bias may have approximately 8-µF effective capacitance in a 1210 (3225 metric) case size and about 6 µF in a 1206 (3216 metric) case size. As another example, a 10-µF, X7R, 16-V rated capacitor in a 1210 (3225 metric) case size used at 12-V DC bias may have approximately 5.5 µF effective capacitance. Check the capacitor specifications published by the manufacturer.