ACT8810
Active- Semi
Rev 4, 01-Oct-09
ActivePathTM CHARGER
FUNCTIONAL DESCRIPTION CONT’D
Table 20:
Thermal Regulation
Charging Status Indication Table
The ACT8810's ActivePath charger features an
internal thermal regulation loop that reduces the
charging current as necessary to ensure that the
die temperature does not rise beyond the thermal
regulation threshold of 110°C. This feature protects
the against excessive junction temperature and
makes the device more accommodating to
aggressive thermal designs. Note, however, that
attention to good thermal designs is required to
achieve the fastest possible charge time by
maximizing charge current.
STATE
Charging
nSTAT
ON
Discharging
Charging Complete
Input Floating
Fault
OFF
OFF
OFF
OFF
In order to account for the reduced charge current
resulting from operation in thermal regulation mode,
the charge timeout periods are extended
proportionally to the reduction in charge current.
Input Supply Detection
The ACT8810's ActivePath charger is capable of
withstanding voltages of up to 12V, protecting the
system from fault conditions such as input voltage
transients or application of an incorrect input
supply. Although the ACT8810 can withstand a
wide range of input voltages, valid input voltages for
charging must be greater than the under-voltage
lockout voltage (UVLO) and the over-voltage
protection (OVP) thresholds, as described below.
Charging Safety Timers
The ACT8810 features a safety timer that is
programmable via an external resistor (RBTR
)
connected from BTR to GA. The timeout period is
calculated as a function of this resistor by the
following equation:
Under Voltage Lock Output (UVLO)
tCHG = KBTR × RBTR, where KBTR = 0.24s/ꢀ.
Whenever the input voltage applied to CHG_IN falls
below 3.0V (typ), an input under-voltage condition is
detected and the charger is disabled. Once an input
under-voltage condition is detected, the input must
exceed the under-voltage threshold by at least
800mV for charging to resume.
If the timeout period expires prior to charge
termination, the charger is disabled and the nSTAT
pin signal a fault condition. If the ACT8810 detects
that the charger remains in precondition for longer
than the precondition time out period (which
determined as tCHG/3), the ACT8810 turns off the
charger and generate a FAULT to ensure prevent
charging a bad cell.
Over Voltage Protection (OVP)
If the charger detects that the voltage applied to
CHG_IN exceeds 6.8V (typ), an over-voltage
condition is detected and the charger is disabled.
Once an input over-voltage condition is detected,
the input must fall below the OVP threshold by at
least 350mV for charging to resume.
Charging Status Indication
The ACT8810 provides one charge-status output,
nSTAT which indicates charge status as defined in
Table 20. nSTAT is open-drain output with internal
5mA current limits, which sinks current when
asserted and are high-Z otherwise, and is capable
of directly driving LED without the need of current-
limiting resistor or other external circuitry. To drive
an LED, simply connect the LED between nSTAT
pin and an appropriate supply (typically VSYS). For
a logic level indication, simply connect a resistor
from nSTAT to a appropriate voltage supply.
Reverse Leakage Current
The ACT8810's ActivePath charger includes
internal circuitry that eliminates the need for
blocking diodes, reducing solution size and cost as
well as dropout voltage relative to conventional
battery chargers. When the voltage at CHG_IN falls
below VBAT, the charger automatically reconfigures
its power switch to minimize current drain from the
battery.
Innovative PowerTM
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ActivePMUTM and ActivePathTM are trademarks of Active-Semi.
I2CTM is a trademark of Philips Electronics.
Copyright © 2009 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
