8.2.2.2 Output Capacitor Selection

The LM36010 is designed to operate with a 10-µF ceramic output capacitor. When the boost converter is running, the output capacitor supplies the load current during the boost converter on-time. When the NMOS switch turns off, the inductor energy is discharged through the internal PMOS switch, supplying power to the load and restoring charge to the output capacitor. This causes a sag in the output voltage during the on-time and a rise in the output voltage during the off-time. Therefore, choose the output capacitor to limit the output ripple to an acceptable level depending on load current and input or output voltage differentials and also to ensure the converter remains stable.

Larger capacitors such as a 22-µF or capacitors in parallel can be used if lower output voltage ripple is desired. To estimate the output voltage ripple considering the ripple due to capacitor discharge (ΔV_Q) and the ripple due to the capacitors ESR (ΔV_ESR), use Equation 4 and Equation 5:

For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:

Equation 4.

The output voltage ripple due to the output capacitors ESR is found by:

Equation 5.

In ceramic capacitors, the ESR is very low so the assumption is that 80% of the output voltage ripple is due to capacitor discharge and 20% from ESR. Table 2 lists different manufacturers for various output capacitors and their case sizes suitable for use with the LM36010.