ACT2801/ACT2801C
Rev 2, 15-Apr-14
FUNCTIONAL DESCRIPTION
Figure 2:
ACT2801C System Operation Flow Chart
at a reduced current, 10% of the programmed
maximum fast charge constant current. Once VBAT
Input Current Limit
reaches the precondition threshold voltage the state
machine jumps to the fast charge state.
When the input current reaches the programmed
value, switch Q1 goes into linear mode and output
voltage starts to drop. When output voltage drops to
4.25V, hiccup mode is triggered and switch Q1
turns off and restart in 2 seconds.
Fast Charge
If battery voltage is above preconditioning
threshold, buck converter charges battery with
constant current. In fast charge state, the ACT2801/
ACT2801C charges at the current set by the
external resistor connected at the ICST pin. During
a normal charge cycle fast charge continues in CC
mode until VBAT reaches the charge termination
voltage, at which point the ACT2801/ACT2801C
charges in top off state.
Switching Battery Charger
ACT2801/ACT2801C is configured in charge mode
(buck mode) when VIN is valid. In this mode, a
battery is charged with preconditioning, fast charge,
top-off and end of charge (EOC). The typical charge
management is shown in Figure 3 and Figure 4.
CC/CV Regulation Loop
Top Off
There are CC/CV regulation loops built in ACT2801/
ACT2801C, which regulates either current or
voltage as necessary to ensure fast and safe
charging of the battery. In a normal charge cycle,
this loop regulates the current to the value set by
the external resistor at the ICST pin. Charging
continues at this current until the battery cell voltage
reaches the termination voltage. At this point the
CV loop takes over, and charge current is allowed
to decrease as necessary to maintain charging at
the termination voltage.
With the battery voltage approaches the EOC
voltage set by the BTV pin. Charge current
decreases as charging continues. In the top off
state, the cell is charged in constant voltage (CV)
mode. During a normal charging cycle charging
proceeds until the charge current decreases below
the end of charge (EOC) threshold, defined as 13%
of fast charge current. When this happens, the state
machine terminates the charge cycle and jumps to
the EOC state.
End of Charge
Precondition Charge
When charges current decreases to 13% of set fast
charge current, the buck converter goes into end of
charge mode and keep monitoring the battery
voltage.
A new charging cycle begins with the precondition
state, and operation continues in this state until VBAT
exceeds the precondition threshold voltage. When
operating in precondition state, the cell is charged
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