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

43 of 97

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ACT2861

30V Buck-Boost Charger with Integrated MOSFETs and OTG

®

Where VOTG_VOUT[9:0] is the decimal equivalent of

the

value

in

this

register.

For

example,

if

OTG_VOUT[9:0] = 0111000100b (452 decimal), the

output voltage = 2.96V + 0.02V * 452 = 12.00V.

When changing from one OTG output voltage to an-

other, the slew rate is programmable between 1V/ms

and 0.1V/ms by I2C bits OTG_OUTPUT_SLEW[1:0] in

register 0x10h. This allows the output to conform to

QC2.0/QC3.0/USB PD functions for higher output volt-

ages.

The battery voltage must always stay above the mini-

mum

allowable battery

voltage set by I2C bits

VBAT_LOW[6:0]

in

register

0x1Ah

and

OTG_VBAT_CUTOFF[2:0] in register 0x0Fh. The ac-

tual voltage is the VBAT_LOW voltage minus the

OTG_VBAT_CUTOFF voltage. If the battery voltage

drops below this value, the IC turns off the OTG output

and goes to the OTG_RST state.

OTG Active Discharge

When changing the OTG output voltage to a higher level,

the switcher ramps the output voltage by the pro-

grammed slew rate. When the output voltage is pro-

grammed from a higher to a lower voltage, the voltage

drops at a rate determined by the output capacitance

and the load current. To minimize the fall time in no-load

conditions, the ACT2861 can provide a 70mA sink when

the output is transitioning to a lower output voltage. En-

able this feature by writing 1 into I2C bit OTG_PULL-

DOWN_RAMP. The 70mA load turns on until the output

voltage goes into regulation.

OTG Enable Delay

Once the OTG has the valid conditions for startup, the

OTG Enable Delay timer is enabled. The timer options

allow a 0ms to 1s delay. The OTG startup delay is con-

trolled by the I2C bits OTG_EN_DLY[1:0]

OTG Mode Soft Start

After the OTG Enable Delay has completed, the IC

starts the output using a soft start function programma-

ble by the I2C bits OTG_SS in register 0x0Eh. The

softstart time is independent of the output voltage set-

ting.

OTG Mode Constant Output Current

Regulation

After OTG mode soft start has completed, the IC moni-

tors the current on VIN input side sense resistor (ISRP

and ISRN) to provide constant current protection and

regulation in OTG mode. When the OTG output current

exceeds programmed value set by the ILIM pin and the

OTG_CC register, the switching converter changes to

output constant current mode and regulates a fixed out-

put current. In this case, the output voltage may drop if

the load resistance continues to decrease.

The maximum OTG output current is set by the same

resistor as the charger input current, Rcs_IN. Rcs_IN must

be set for the larger of the charge current or OTG cur-

rent. The maximum allowable OTG output current is 5A.

The actual output current limit, IOTG_OUT_LIM can be

scaled between 1% to 100% of IILIM in 1% steps. The

following equation defines the final OTG output current

limit.

������������������������������������������������_������������������������������������_������������������������������������=������������������������������������������������������������∗������������������������������������_������������������������[6:0]

Where IILIM is the hardware programmed current limit

(see the Charging – Maximum Input Current section

for details) and OTG_CC[6:0] is the scaling factor.

OTG_CC[6:0] is the decimal equivalent value in this

register. For example, if IILIM, is programmed to 5A and

OTG_CC[6:0] = 0111100b (60% decimal), the final

charge current = 5A * 0.60 = 3A.

Note that OTG_CC[6:0] is a 7 bit register and can be

programmed between 0x00h and 0x7Fh (0% and

127%). If a value of 0x00h is written to the register, the

register retains 0x00h, but the IC sets the OTG scaling

factor to 1%. If a value above 0x64h (100%) is written

to the register, the IC retains the value, but sets the scal-

ing factor to 100%

The OTG regulation mode can be monitored in real time

by I2C bit OTG_Output_CC in register 0x20h. When this

bit = 0, the IC is regulating in output constant voltage

mode. When this bit = 1, the IC is regulating in constant

current mode. If the output drops below 3V, the IC as-

sumes an output fault has occurred and disables the

output for 3s. This is the OTG_HICCUP state. After 3s,

the state machine goes to OTG_RST and restarts. If a

short or high current fault is present after the restart, the

IC cycles back to OTG_HICCUP and OTG_RST. This

cycle continues indefinitely until OTG is disabled or the

fault is removed.

OTG Mode Constant Input Current Regulation

At all times during OTG mode, the IC monitors the cur-

rent on VBAT output side sense resistor (OSRP and

OSRN) to provide battery current protection.

The maximum OTG input current is set by the same re-

sistor as the charger output current, RCS_OUT. Unlike the

RCS_IN resistor, RCS_OUT does not have to be set to the

larger of the charge current or OTG input current. The

maximum allowable OTG input current is 5A. The max-

imum OTG input current limit, IOTG_IN_LIM, is a scaled ver-

sion of the programmed charge current, ICHG. IOTG_IN_LIM

is scaled to 150% or 200% of ICHG. This allows a larger

battery discharge current than charge current. The I2C