ACT8937A
Rev 1, 22-Oct-12
Thermal Regulation
Table 13:
The charger features an internal thermal regulation
loop that monitors die temperature and reduces
charging current as needed to ensure that the die
temperature does not exceed the thermal regulation
threshold of 110°C. This feature protects 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.
Total Safety Timer Setting
TOTAL TIME-OUT
PERIOD
TOTTIMO[1] TOTTIMO[0]
0
0
1
1
0
1
0
1
3 hrs
4 hrs
5 hrs
Disabled
Charge Safety Timers
Charge Status Indicator
The charger features programmable charge safety
timers which help ensure a safe charge by
detecting potentially damaged cells. These timers
are programmable via the PRETIMO[1:0] and
TOTTIMO[1:0] bits, as shown in Table 12 and Table
13. Note that in order to account for reduced charge
current resulting from DCCC operation, the charge
time-out periods are extended proportionally to the
reduction in charge current. As a result, the actual
safety period may exceed the nominal timer period.
The charger provides a charge-status indicator
output, nSTAT. nSTAT is an open-drain output
which sinks current when the charger is in an
active-charging state, and is high-Z otherwise.
nSTAT features an internal 8mA current limit, and is
capable of directly driving a LED without the need
of a current-limiting resistor or other external
circuitry. To drive an LED, simply connect the LED
between nSTAT pin and an appropriate supply,
such as VSYS. For a logic-level charge status
indication, simply connect a resistor from nSTAT to
an appropriate voltage supply.
Charger Timer Interrupts
The charger features the ability to generate
interrupts based upon the status of the charge
Table 14:
Charging Status Indication
timers. Set the TIMRPRE[
]
bit to
1
and
TIMRSTAT[ ] bit to 1 to generate an interrupt when
the Precondition Timer expires. Set the TIMRTOT[ ]
bit to 1 and TIMRSTAT[ ] bit to 1 to generate an
interrupt when the Total-Charge Timer expires.
STATE
PRECONDITION
FAST-CHARGE
TOP-OFF
nSTAT
Active
Active
Active
High-Z
High-Z
High-Z
High-Z
TIMRDAT[ ] indicates the status of the charge
timers. A value of 1 indicates a precondition time-
out or a total charge time-out occurs, a value of 0
indicates other cases.
END-OF-CHARGE
SUSPEND
When an interrupt is generated by the charge
timers, reading the TIMRSTAT[ ] returns a value of
1. TIMRSTAT[ ] is automatically cleared to 0 upon
reading. When no interrupt is generated by the
charge timers, reading the TIMRSTAT[ ] returns a
value of 0.
TEMPERATURE FAULT
TIME-OUT-FAULT
Reverse-Current Protection
The charger includes internal reverse-current
protection 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 CHGIN falls
below VBAT, the charger automatically reconfigures
its power switch to minimize current drawn from the
battery.
Table 12:
PRECONDITION Safety Timer Setting
PRECONDITION
PRETIMO[1] PRETIMO[0]
TIME-OUT PERIOD
0
0
1
1
0
1
0
1
40 mins
60 mins
80 mins
Disabled
Battery Temperature Monitoring
In a typical application, the TH pin is connected to
the battery pack's thermistor input, as shown in
Innovative PowerTM
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ActivePMUTM and ActivePathTM are trademarks of Active-Semi.
I2CTM is a trademark of NXP.
Copyright © 2012 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
