CC864-DUAL Hardware User Guide
1vv0300791 Rev 4.4 – 2011-01-26
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights Reserved.
Page 28 of 63
During constant current charging the battery is charged with a constant current of
600mA.
As the battery voltage rises and approaches its desired value of 4.2V the charging
current begins to decrease, indicating the end of constant current charging and the
beginning of residual charging.
The firmware monitors the voltage and takes the appropriate action to terminate
constant current charging mode. Charging continues with residual charging (either
constant voltage or pulsed).
Note:
In this application the charging firmware limits the charging current to 600mA.
3.3.4.3.
Constant Voltage Charging
Once constant current charging of the lithium-ion battery is finished, the charging
continues using either constant voltage or pulsed techniques.
Constant voltage charging is similar to the constant current mode: The battery
voltage is constant while the charging current decreases exponentially for the
remaining charging process.
The end of the constant voltage charging is typically detected by allowing voltage
operation for a pre-determined duration beyond crossing the VBATDET threshold in
the internal charger IC (lasting for one and a half to two hours).
The firmware limits the predetermined duration to 120 minutes because charging for
too long can damage the battery.
3.3.4.4. Pulse
Charging
The CC864-DUAL uses pulse charging for final charging.
Pulse charging is implemented by switching the pass transistor on the internal
charger IC on and off.
The module and external electronics must draw minimal current so the battery’s open
circuit voltage can be measured accurately during the off interval.
Compared to constant voltage charging, pulse charging:
Provides better voltage accuracy
Reaches full charge more quickly
Dissipates less transistor power when switching from constant current
charging
Pulse charging is enabled through firmware control and uses the same hardware as
constant current or constant voltage charging, but repeatedly opens and closes the
pass transistor to deliver current pulses to the battery.
One purpose of pulsed operation is to check and recheck the battery’s open circuit
voltage, confirming a full charge before terminating the process.