ACT88321

Advanced PMIC with 3 Bucks, 2 LDOs, and Load Bypass Switches

Datasheet Rev. D , June 17, 2022 | Subject to change without notice

38 of 55

www.qorvo.com

®

capacitor and from the capacitor to PGNDx should as

short and wide as possible.

Inductor Selection

The ACT88321 buck converters are optimized for oper-

ation with 0.47

μH to 1μH inductors. Choose an inductor

with a low DC resistance and avoid inductor saturation

by choosing inductors with DC ratings that exceed the

maximum output current by at least 30%. The following

equation calculates the inductor ripple current.

∆������������������������ =�1−�������������������������������������������������������������������������������������∗������������������������������������������������

������������������������������������∗������������

Where VOUT is the output voltage, VIN is the input volt-

age, FSW is the switching frequency, and L is the induc-

tor value.

Output Capacitor Selection

The ACT88321 is designed to use small, low ESR,

ceramic output capacitors. Buck1/2 typically require a

22µF output capacitor while Buck3 typically requires a

10µF capacitor. To ensure stability, the actual Buck1/2

capacitance must be greater than 12µF while Buck3

must be greater than 6µF. There is no maximum output

capacitance limitation. Design for an output ripple volt-

age less than 1% of the output voltage. The following

equation calculates the output voltage ripple as a func-

tion of output capacitance.

VRIPPLE

= ∆������������������������

8∗������������������������������������∗������������������������������������������������

Where ΔIL is the inductor ripple current, FSW is the

switching frequency, and COUT is the output capacitance

after taking DC bias into account.

Be sure to consider the capacitor’s DC bias effects and

maximum ripple current rating when using capacitors

smaller than 0805.

A capacitor’s actual capacitance is strongly affected

by its DC bias characteristics. The output capacitor is

typically an X5R, X7R, or similar dielectric. Use of Y5U,

Z5U, or similar dielectrics are not recommended due to

their wide variation in capacitance over temperature and

voltage ranges.

Unused Buck Outputs

If a buck converter is not used, connect the VIN_Bx pin

to the other VIN_Bx pins. Connect FB_Bx to AGND.

Leave SWx open. The input and output capacitors are

not needed.