AP63200/AP63201/AP63203/AP63205

12

Output Capacitor

The output capacitor keeps the output voltage ripple small, ensures feedback loop stability, and reduces the overshoot/undershoot of the output

voltage during load transients. During the first few milliseconds of a load transient, the output capacitor supplies the current to the load. The

converter recognizes the load transient and sets the duty cycle to maximum but the current slope is limited by the inductor value.

The ESR of the output capacitor dominates the output voltage ripple. The amount of ripple can be calculated from Eq. 9:

Eq. 9

An output capacitor with large capacitance and low ESR is the best option. For most applications, a 22µF to 68µF ceramic capacitor is sufficient.

(

Eq. 10

Where

ΔV is the maximum output overshoot voltage.

13

Bootstrap Capacitor

To ensure the proper operation, a ceramic capacitor must be connected between the BST and SW pins. A 100nF ceramic capacitor is sufficient. If

the BST capacitor voltage falls below 2.3V, the boot undervoltage protection circuit turns Q2 on for 220ns to refresh the BST capacitor and raise its

voltage back above 2.85V. The BST capacitor voltage threshold is always maintained to ensure enough driving capability for Q1. This operation

may arise during long periods of no switching such as in PFM with light load conditions. Another event requires the refreshing of the BST capacitor

is when the input voltage drops close to the output voltage. Under this condition, the regulator enters low dropout mode by holding Q1 on for

multiple clock cycles. To prevent the BST capacitor from discharging, Q2 is forced to refresh. The effective duty cycle is approximately 100% so that

it acts as an LDO to maintain the output voltage regulation.

AP63200/AP63201/AP63203/AP63205

Document number: DS41326 Rev. 2 - 2

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January 2019

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