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KTZ8866

January 2022 - Revision 04b

Page 35 of 37

Company Confidential

Flying Capacitor Selection for Bias

The charge pump needs an external flying capacitor. The minimum value for smartphone application is 4.7

μF

and 10

μF for tablet application. Special care must be taken while choosing the flying capacitor as it will directly

impact the output voltage accuracy and load regulation performance.

Inductor Selection for Dual Output Bias

An inductor in the range of 2.2µH to 10µH with low DCR can be selected for the boost converter. To estimate

the inductance required for applications, calculate the maximum input average current as the following

Where, η is the converter efficiency and can be approximated as 90% for the typical case. In order to have

smaller current ripple (to improve efficiency and minimize output voltage ripple), larger inductance will be

required. If inductor ripple current needs to be less than 40% of the average input current, then

Where duty cycle can be estimated as

Then

Therefore, the inductance can be calculated as

Where, fS is the switching frequency of the boost converter.

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