ACT2861 datasheet(29/97 Pages) QORVO

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Data Sheet Rev. F, April 2022 | Subject to change without notice

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ACT2861

30V Buck-Boost Charger with Integrated MOSFETs and OTG

BUCK-BOOST OPERATION

The ACT2861 is a monolithic buck-boost charger with

On-The-Go (OTG). As a result, it can operate in both

charge mode and OTG mode. In charge mode, the IC

converts power from VIN to VBAT to charge a 2S to 5S

battery. In OTG mode, it converts power from the bat-

tery to VIN to provide a regulated output voltage. Four

internal, low resistance, NMOS switches minimize the

application circuit size and reduce power losses to max-

imize efficiency. Internal high side gate drivers, which

require only two small external capacitors, further sim-

plify the design process. An advanced switch control al-

gorithm allows the buck-boost converter to maintain

charge or OTG output voltage regulation with input volt-

ages that are above, equal to, or below the regulated

output voltage. The ACT2861 automatically transitions

between these three operating modes, depending on

the input to output voltage ratios.

Power Stage

Figure 6 shows the 4-switch, buck-boost power stage.

The converter operates with current mode control. The

internal control algorithm reconfigures the IC between a

buck, a boost, and a buck-boost topology as needed.

This reduces power dissipation and maximizes effi-

ciency because only two FETs switch when in it oper-

ates in buck or boost mode. Table 2 shows the switch

configuration in each topology. Note that this table is

valid for Charge mode. In OTG mode, power flows in

the opposite direction, so the switching modes are re-

versed. The voltage transition between buck to buck-

boost and from buck-boost to boost modes is set by I2C

bits XOVER_ADJ_BUCK and XOVER_ADJ_BOOST.

With a fixed input voltage and an increasing battery volt-

age, the IC switches from buck mode to buck-boost

mode when VIN – VBAT < XOVER_AJD_BUCK, which

is typically 1V. It switches from buck-boost to boost

mode when VBAT – VIN > XOVER_ADJ_BOOST,

which is typically 2V. These values are set at the factory

to optimize efficiency and performance for each CMI.

The power stage is bi-directional and provides power in

both directions. When charging, power flows from VIN

to VBAT. In OTG mode, power flows from VBAT to VIN.

Q1-Q4 are all internal, N-ch MOSFETs to minimize size

and maximize efficiency.

VIN

VBAT

SW1

SW2

Figure 6: 4-Switch Buck-Boost Power Stage

Table 2: Buck-Boost Switch Configuration

CHARGE MODE

BUCK

BUCK-

BOOST

SWITCHING

OFF

SWITCHING

Figure 7 shows the power stage operating modes. A

typical example of how the converter switches between

modes can be explained with an example using a 15V

input source to charge a 4S Li-Ion battery. When fully

discharged, the battery voltage is 12V. With VIN=15V

and VBAT=12V, the control loop operates in Buck mode

at point A. As the battery charges, the operating mode

maintains buck mode until it crosses the threshold be-

tween buck mode and buck-boost mode. When the bat-

teries are charged at 15V, the control loop operates at

point B in Buck-Boost mode. The 4S battery reaches

charge termination voltage at 17.4V. In this case, the

control loop operates at point C, which is still Buck-

Boost mode. If the input voltage dropped from 15V to

12V, the control loop will move to point D and operate

in Boost mode.

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