ACT2823 datasheet(13/25 Pages) ACTIVE-SEMI

13 / 25 page

ACT2823

REV 1, 01-DEC-2016

Innovative PowerTM

ActiveSwitcherTM

is a trademark of Active-Semi.

The following table provides the recommended RICST

values based on RCS=25mΩ and 50mΩ.

IC (A)

RICST

Units

RCS=25mΩ

RCS=50mΩ

0.8

kΩ

0.9

8.89

4.44

kΩ

1.1

7.27

3.64

kΩ

1.2

6.67

3.33

kΩ

1.3

6.15

3.08

kΩ

1.4

5.71

2.86

kΩ

1.5

5.33

2.67

kΩ

Top Off

When the battery voltage reaches the End-of-Charge

Voltage, the ACT2823 transitions to Top Off mode. Top

Off mode charges the battery with a constant voltage.

In Top Off mode, the charging current slowly decreases

as the actual battery voltage increases and the voltage

across the battery’s ESR decreases. The charger stays

in Top Off mode until the charging current drops below

the EOC (End-of-Charge) current which is 10% of the

programmed fast charge current. At this point the

battery is considered fully charged and the charger

transitions into the End of Charge mode.

End-of-Charge

When the charging current drops to 10% of the fast

charge current, the charger enters End-of-Charge mode.

If register 0x04h, bit 7 = 0, the charger immediately turns

off. If this bit = 1, the charger continues to charge in

constant voltage mode for 45 minutes. In this case, the

charge current continues to drop while the battery

voltage is held at the End-of-Charge voltage. If the

battery voltage drops below 95% of the End-of-Charge

voltage, the charger transitions back into Top Off mode.

The charger automatically transitions between these

four charging modes as the battery voltage increases

and decreases during charging and discharging cycles.

If a battery is not present during charging mode, the

charger regulates its output to the End-of-Charge

voltage. If a battery is then connected, the charger

automatically transitions to the proper operating mode

that is appropriate for the battery’s voltage. If the battery

disconnected from the charger, it regulates its output to

the End-of-Charge voltage

Thermal Regulation

The charger contains a thermal regulation feature that

prevents the IC from reaching thermal shutdown in high

temperature environments. It works in both charge and

discharge modes. The charger operates at full charging

current when the ACT2823 die temperature is below

110°C. If the die temperature increases above 110°C,

the IC reduces charging current at a rate of -10%/°C.

This ensures that the output voltage on VOUT has

priority over charging the battery. In discharge mode,

the IC delivers full current at rated voltage when the

temperature is below 130°C. If the die temperature

increases above 130°C, the IC decreases the output

voltage by -115mV/°C.

End-of-Charge Timer

When the charger enter the End-of-Charge mode, it

either immediately stops charging or continues to

charge for 45 minutes. If register 0x04h, bit 7 = 0, the

charger immediately turns off. If this bit = 1, the charger

continues to charge in constant voltage mode for 45

minutes.

Power Path Priority

The ACT2823 always gives priority to the system

voltage on VOUT. If the input voltage source is current

limited and cannot simultaneously provide the full

charge current plus the full system current (current out

of VOUT), the input voltage would drop and cause a

brownout situation on VOUT. The ACT2823 avoids the

brownout condition by reducing the charging current if

the input voltage drops. If the IC detects that a USB

cable is connected, the Charge Current Foldback

Threshold voltage starts at 4.92V. If no USB cable is

detected, the starting voltage is 4.7V. The charger

linearly reduces charge current from full charge current

to 0A as the voltage on VIN drops from 4.7V to 4.6V or

from 4.92V to 4.82V, depending on whether or not a

USB cable is detected.

The charger also reduces the charging current if the

total input current (charging current plus system current)

exceeds 80% of the programmed input current limit

(ILIM) threshold of 3.8A. Charging current is linearly

reduced from full charge current to 0A as the input

current increases from 80% of ILIM to 100% of ILIM.

Operating Modes

The ACT2823 automatically switches between several

different operating modes, depending on circuit

conditions.

Charge Mode

When input power is applied and there are no faults, the

IC operates in Charge Mode. Charge Mode turns on Q1

to power VOUT with the input voltage. Note that Q1

stays off and VOUT is not present in Trickle Charge

mode. Charge mode configures the switches Q2 and

Q3 as a boost converter to charge the battery. The IC

automatically enters Charge Mode when input power is

applied. There is a 2s delay when transitioning from

Discharge Mode to charge mode. During this time, the

IC goes into HZ mode

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