ACT86600

Hybrid PMIC for Enterprise

Storage and Computing

Data Sheet Rev. B, February 2, 2023

Subject to change without notice

49 of 56

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Table 10. Buck-Boost Peak Current Threshold Settings

ILIM[1:0]

QSW5_top FET Peak

Current (A)

00

1.2

01

1.7

10

2.1

11

2.5

If the peak current reaches 80% of the programmed

threshold for 16 consecutive switching cycles and the

IWARN_INT_MASK bit = 0, the IC asserts nIRQ low and

changes the I2C bit ILIM_WARN = 1. It continues to

operate normally in this condition.

If the peak current reaches the programmed threshold

and the I2C bit IFLT_INT_MASK bit = 0, the IC turns off

the power FET for that switching cycle.

If the peak

current reaches the threshold 16 consecutive switching

cycles, the IC asserts nIRQ low. This condition typically

results in shutdown due to an UV condition due to the

shortened switching cycle. A short circuit condition that

results in the peak switch current being 125% of

ILIM_SET immediately shuts down the supply and

asserts nIRQ low if the I2C bit SHUT_INT_MASK = 0.

The supply tries to restart in 14ms. If the fault condition

is not masked, the IC transitions to the OVUV State,

turns off all supplies, and restarts the system in 100ms.

Compensation

The Buck-boost utilizes a proprietary internal compen-

sation scheme to simultaneously simplify external com-

ponent selection while optimizing transient performance

over their full operating range. No external compensa-

tion design is required. Simply follow a few simple

guidelines described below when choosing the output

capacitor and inductor.

Input Capacitor Selection

The input requires a high quality, low-ESR, ceramic

input capacitor. The Buck-boost input voltage can be

connected to the same or a different voltage rail from

the other converters. Even if it is connected to the same

voltage rail, it must have a dedicated input capacitor.

10µF capacitors are typically suitable, but this value can

be increased without limit. Smaller capacitor values can

be used with lighter output loads. Choose the input

capacitor value to keep the input voltage ripple less than

50mV. When in buck-mode, the following equations

calculates the input ripple.

Vripple

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

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 input capacitor is

typically an X5R, X7R, or similar dielectric. Use of Y5V,

Z5U, or similar dielectrics is not recommended. Be sure

to consider the capacitor’s DC bias effects and

maximum ripple current rating when using capacitors

smaller than 0805. Input capacitor placement is critical

for proper operation. The input capacitor must be placed

as close to the IC as possible. The traces from the

VBBST pin to the capacitor and from the capacitor to

PGNDx should as short and wide as possible.

Inductor Selection

The

Buck-boost

uses

a

proprietary

internal

compensation

scheme

to

simultaneously

simplify

external component selection and optimize transient

performance

over

its

full

operating

range.

The

ACT86600 Buck-boost regulator is optimized for a

4.7µH to 6.8

μH range. Choose inductors with a low DC-

resistance, or DCR, for higher efficiency and avoid

inductor saturation by choosing inductors with DC

ratings that exceed the maximum inductor peak current

by at least 30%. Additionally, the inductor peak-to-peak

current ripple must be carefully considered along with

the selected switching frequency before selecting

appropriate inductor values with adequate current rating.

The following equations calculate the inductor ripple

current in buck-only and boost-only modes.

∆IL(Buck−only)=�1−VOUTVIN�∗VOUT

FSW∗L

∆IL(Boost−only)=�1−VINVOUT�∗VIN

FSW∗L

The buck-boost ripple current is the higher of the two

following equations.

∆IL(Buck−boost)=�1−0.7∗VVINVOUT�∗VIN

FSW∗L

∆IL(Buck−boost)=0.3∗VVOUT

FSW∗L