9.2.2.7 Output Capacitor Selection

For small output voltage ripple, TI recommends a low-ESR output capacitor like a ceramic capacitor. Typically, three 22-μF ceramic output capacitors work for most applications. Higher capacitor values can be used to improve the load transient response. Take care when evaluating a capacitor’s derating under DC bias. The bias can significantly reduce capacitance. Ceramic capacitors can lose most of their capacitance at rated voltage. Therefore, leave margin on the voltage rating to ensure adequate effective capacitance. From the required output voltage ripple, use the following equations to calculate the minimum required effective caapctance C_OUT:

Equation 11.

Equation 12.

where

• V_{ripple_dis} is output voltage ripple caused by charging and discharging of the output capacitor.
• V_{ripple_ESR} is output voltage ripple caused by ESR of the output capacitor.
• V_{IN_MIN} is the minimum input voltage of boost converter.
• V_OUT is the output voltage.
• I_OUT is the output current.
• I_Lpeak is the peak current of the inductor.
• ƒ_SW is the converter switching frequency.
• R_{C_ESR} is the ESR of the output capacitors.