AAT3680
Lithium-Ion Linear Battery Charge Controller
it has not yet reached 4.2V to complete the charge
cycle. If the battery is removed and then placed back
Sleep Mode
When the input supply is disconnected, the charger
automatically enters power-saving sleep mode. Only
consuming an ultra-low 2µA in sleep mode, the
AAT3680 minimizes battery drain when it is not
charging.This feature is particularly useful in applica-
tions where the input supply level may fall below the
battery charge or under-voltage lockout level. In such
cases where the AAT3680 input voltage drops, the
device will enter the sleep mode and automatically
resume charging once the input supply has recov-
ered from its fault condition. This makes the AAT3680
well suited for USB battery charger applications.
on the charger, the charge cycle will not resume until
the battery voltage drops below the VRCH threshold.
In another case, a battery under charge is in the
constant current mode and the cell voltage is 3.7V
when the input supply is inadvertently removed
and then restored. The battery is below the VRCH
threshold and the charge cycle will immediately
resume where it left off.
LED Display
Charge Status Output
Charge Inhibit
The AAT3680 provides a battery charge status output
via the STAT pin. STAT is an open-drain serial data
output capable of displaying five distinct status func-
tions with one LED connected between the STAT pin
and VP. There are four periods which determine a
status word. Under default conditions each output
period is one second long; thus one status word will
take four seconds to display through an LED.
The AAT3680 charging cycle is fully automatic;
however, it is possible to stop the device from
charging even when all conditions are met for
proper charging. Switching the TS pin to either VP
or VSS will force the AAT3680 to turn off the pass
device and wait for a voltage between the low and
high temperature voltage thresholds.
The five modes include:
Resuming Charge and the VRCH
Threshold
1. Sleep/Charge Complete: The IC goes into
Sleep mode when no battery is present -OR- When
the charge cycle is complete.
The AAT3680 will automatically resume charging
under most conditions when a battery charge cycle is
interrupted. Events such as an input supply interrup-
tion or under voltage, removal and replacement of the
battery under charge or charging a partially drained
battery are all possible. TheAAT3680 will monitor the
battery voltage and automatically resume charging in
the appropriate mode based upon the measured bat-
tery cell voltage. The feature is useful for systems
with an unstable input supply which could be the case
when powering a charger from a USB bus supply.
This feature is also beneficial for charging or "topping
off" partially discharged batteries.
2. Fault: When an Over-Current (OC) condition is
detected by the current sense and control circuit -
OR- When an Over-Voltage (OV) condition is
detected at the BAT pin -OR- When a battery Over-
Temperature fault is detected on the TEMP pin.
3. Battery Conditioning: When the charge system
is in the 1X or 2X trickle charge mode
4. Constant Current (CC) Mode: When the system
is in the constant current charge mode.
5. Constant Voltage (CV) Mode: When the system
is in the constant voltage charge mode.
The only restriction on resuming charge of a bat-
tery is the battery cell voltage must be below the
battery recharge voltage threshold (VRCH) specifi-
cation. There is VRCH threshold hysteresis built into
the charge control system. This is done to prevent
the charger from erroneously turning on and off
one a battery charge cycle is complete.
An additional feature of the LED status display is
for a Battery Not Detected state. When the
AAT3680 senses there is no battery connected to
the BAT pin, the STAT output will turn the LED on
and off at a rate dependant on the size of the out-
put capacitor being used. The LED cycles on for
two periods then remains off for two periods. See
figure 2 below.
For example, the AAT3680-4.2 has a typical VRCH
threshold of 4.1V. A battery under charge is above
4.1V, but is still in the constant voltage mode because
3680.2003.4.0.91
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