ACT3704
Rev2, 26-Jul-07
For a logic-level indication, simply connect a resistor
from each output to an appropriate voltage supply.
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 charging continues.
Reverse Battery & Shutdown
The ACT3704 includes internal circuitry that elimi-
nates the need for series blocking diodes, reducing
solution size and cost as well as dropout voltage
relative to conventional battery chargers. When VIN
goes below the ACT3704’s under voltage-lockout
(UVLO) voltage, or when VIN drops below VBAT, the
ACT3704 automatically goes into SUSPEND mode
and reconfigures its power switch to minimize cur-
rent drain from the battery.
If the ACT3704 state machine does not complete a
charging cycle before the TOP-OFF Timeout period
(TTOPOFF) expires, then a damaged cell is detected
and the state machine jumps to the TIMEOUT-
FAULT State.
The TOP-OFF Timeout period is default to 60mins
with a 2.2nF CTIMER capacitor, or it can be increased
with a larger value external capacitor. See the
Safety Timers section for more information.
Safety Timers
The ACT3704 has several internal charge safety
timers, for each of the PRECONDITION and NOR-
MAL charge states as well as TOPOFF timeout pe-
riod. If any of these timers expire before charge suc-
cessfully proceeds through the associated state, the
ACT3704 enters the TIMEOUT-FAULT state. The
TIMEOUT-FAULT state can only be reset by power-
cycling the ACT3704.
In TOP-OFF state, nSTAT indicates charge com-
plete but charge current still continues. After another
delay of 60mins, then charging stops and charge
current becomes zero. When the battery voltage
drops below the charge restart voltage, the charging
process will start again.
End of Charge State
Each of these timers are internally set according to
the following ratios:
In the End of Charge (EOC) state, the ACT3704
presents a high-impedance to the battery, allowing
the cell to “relax” and minimize battery leakage cur-
rent. The ACT3704 continues to monitor the cell
voltage, however, so that it can reinitiate charging
cycles as necessary to ensure that the cell remains
fully charged.
TPRECONDITION =1×TO
TNORMAL =1.5 ×TO
TTOTAL = 3 ×TO
(9)
(10)
(11)
All the timers could be set by an external capacitor
by (CTIMER in nF) where TO is given by:
Charge Restart
Under normal operation, the state machine initiates
a new charging cycle by jumping to the NORMAL
CHARGE state when VBAT drops below the Charge
Termination Threshold by more than the Charge Re-
start Threshold of 100mV (typ).
TO = 9×CTIMER ±15%
(12)
When operating in thermal regulation mode the
timeout periods are extended in order to compen-
sate for the effect of the reduced charging current
on total charge time. In order to ensure a safe
charge, the maximum timeout periods are limited to
2x the room temperature values.
Timeout-Fault State
In TIMEOUT-FAULT state, both nSTAT and nEOC
indicators are OFF, or high-Z.
Charge and EOC Status Outputs
nSTAT and nEOC are open-drain outputs that sink
current when asserted and are high-Z otherwise. For
more information regarding the state of nSTAT and
nEOC throughout the entire charging cycle, see Ta-
ble 3. These outputs have internal 7mA current lim-
its, and are capable of directly driving LEDs, without
the need of current-limiting resistors or other exter-
nal circuitry, for a visual charge-status indication. To
drive an LED, simply connect the LED between
each pin and an appropriate supply (typically VIN).
Innovative Products. Active Solutions.
- 10 -
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