ACT8740
Rev PrB, 25-Feb-08
SINGLE-CELL Li+ BATTERY CHARGER (CHGR)
FUNCTIONAL DESCRIPTION CONT’D
does not reach the Precondition Threshold Voltage
before the Precondition Charge Timeout period ex-
pires, then a damaged cell is detected and the state
machine jumps to the TIMEOUT-FAULT state.
SUSPEND State
When in the SUSPEND state, the charger is dis-
abled and the charger presents a high-impedance
to the battery, but the charge-control circuitry re-
mains functional. When exiting the SUSPEND
state, the charge timer is reset and the state ma-
chine jumps to the PRECONDITION state.
FAST-CHARGE State
In the FAST-CHARGE state the charger operates in
Constant-Current (CC) mode and charges the cell
at the programmed charge current. During a normal
charge cycle, constant-current charging continues
until VBAT reaches the charge termination voltage, at
which point the state machine jumps to the TOP-
OFF state.
TIMEOUT-FAULT State
When a TIMEOUT-FAULT occurs, charging is sus-
pended, CHGR/TIMOFLT[ ] is set to [1], and the
charger presents a high-impedance to the battery.
To maximize safety, there is no direct path to re-
sume charging from the TIMEOUT-FAULT state. A
new charging cycle may only be initiated if the state
machine first jumps to the SUSPEND state then
each of the conditions necessary to enter the PRE-
CONDITION state are satisfied.
TOP-OFF State
In the TOP-OFF state the cell is charged in Con-
stant-Voltage (CV) mode with the charge current
limited by the internal chemistry of the cell, decreas-
ing as the cell charges. A normal charging cycle
continues until the charge current decreases to be-
low the End-Of-Charge (EOC) threshold. In order to
improve immunity to conditions that can result in
false-EOC detection, the charging continues until
the EOC condition persists for 4 consecutive min-
utes. Once this condition is met, the charge cycle is
terminated and the state machine jumps to the
SLEEP state.
SLEEP State
In the SLEEP state the ACT8740 presents a high-
impedance to the battery, allowing the cell to “relax”
and minimizing battery leakage current. The
ACT8740 continues to monitor the cell voltage,
however, so that it can reinitiate a charging cycle as
necessary to ensure that the cell remains fully
charged.
Charge Restart
After a charge cycle successfully terminates, the
ACT8740 jumps to its SLEEP state to minimize bat-
tery drain, but continues to actively monitor the cell
voltage. A new charging cycle begins when the cell
voltage has dropped by 200mV (typ), keeping the
cell fully charged. This charge restart process mini-
mizes cycle-life degradation of the cell by allowing it
to “relax” between charges, while ensuring that the
cell remains fully-charged while connected to a
power source.
Innovative Products. Active Solutions.
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ActivePMUTM is a trademark of Active-Semi.
Copyright © 2008 Active-Semi, Inc.
I2CTM is a trademark of Philips Electronics.
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