ACT8740
Rev PrB, 25-Feb-08
SINGLE-CELL Li+ BATTERY CHARGER (CHGR)
FUNCTIONAL DESCRIPTION
Charger Status
General Description
During normal operation, the processor can read
the status of the input supply by reading
CHGR/VINPOK[ ], which is set to [1] when the fol-
lowing conditions are true:
The ACT8740’s internal battery charger is a full-
featured, intelligent, linear-mode, single-cell charger
for Lithium-based cells. This charger provides a
complete selection of advanced functions and re-
quires minimum system design effort.
1) The voltage at VIN is greater than the voltage at
BAT, and
The core of the charger is a CC/CV (Constant- Cur-
rent/Constant-Voltage), linear-mode charge control-
ler with a highly-accurate charge termination thresh-
old. This controller incorporates current and voltage
sense circuitry, an internal power MOSFET, a full-
featured state-machine that implements charge
control and safety features, and circuitry that elimi-
nates the reverse-blocking diode required by con-
ventional charger designs. The ACT8740’s charger
also features thermal-regulation circuitry that pro-
tects it against excessive junction temperature, al-
lowing the fastest possible charging times, as well
as proprietary input protection circuitry that makes
the charger robust against input voltage transients
that can damage other chargers.
2) The voltage at VIN is greater than the VIN
UVLO threshold.
Alternatively, the processor can read the status of the
charger by reading the CHGR/CHGROK[ ] bit, which
is set to [1] when the following conditions are true:
1) The voltage at VIN is greater than the voltage at
BAT, and
2) The voltage at VIN is greater than the VIN
UVLO threshold, and
3) No fault has occurred.
Finally, the status of a charge cycle can be deter-
mine by reading the CHGR/CHGSTAT[ ] bit or by
evaluating the state of the nSTAT output. nSTAT is
an open-drain output that has an internal 8mA cur-
rent limit, and is capable of directly driving LEDs for
a visual charge-status indication without the need of
current-limiting resistors or other external circuitry.
To drive an LED, simply connect the LED between
an appropriate supply, typically VIN, and nSTAT.
When a logic-level charge status indicator is de-
sired, simply connect a pull-up resistor of 10kꢀ or
more from nSTAT to OUT2 or another suitable sup-
ply.
CC/CV Regulation Loop
At the core of the ACT8740’s battery charger is a
CC/CV regulation loop, which regulates either cur-
rent or voltage as necessary to ensure fast and safe
charging of the battery. In a normal charge cycle,
this loop regulates the charge current to the pro-
grammed charge current level and continues charg-
ing at this current until the battery cell voltage
reaches the charge termination voltage. Once the
cell reaches the Charge-Termination Threshold
Voltage, the CV loop takes over and charge current
is allowed to decrease as necessary to keep the
cell voltage at the charge termination voltage.
CHGR/CHGSTAT[ ] is set to [1] and nSTAT sinks
current when any of the following conditions are
true:
Charger Enable/Disable
1) The charger is operating in the PRECONDI-
TION state, or
When a valid input voltage is applied to VIN, the
battery charger is automatically enabled in order to
simplify system design and eliminate the need for
external input supply detection circuitry.
2) The charger is operating in the FAST-CHARGE
state, or
3) The charger is operating in the TOP-OFF state.
Once the charger is enabled, a charge cycle auto-
matically begins unless CHGLEV is floating,
CHGR/SUSCHG[ ] is set to [1], or a fault condition
has occurred.
When none of these conditions are true, CHGR/
CHGSTAT[ ] is cleared to [0] and nSTAT goes into
a high-Z state.
Innovative Products. Active Solutions.
- 37 -
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Copyright © 2008 Active-Semi, Inc.
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