ACT2804
Rev 2, Feb-04-2016
FUNCTIONAL DESCRIPTION
ACT2804 is a complete battery charging and
discharging power management solution for
applications of dull-cell lithium-based backup
battery pack or power bank.
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 ACT2804 charges in top off state.
With the advanced bidirectional architecture, a
synchronous boost/buck converter is connected
from VOUT to switching node (SW). The converter
could be configured as either boost to charge
battery or buck to discharge battery.
Top Off
Device transitions from Fast Charge (CC) to Top
Off (CV), and moves to EOC (End of Charge) state
when charging current is less than IEOC
.
Modes of Operation
End of Charge
ACT2804 has 3 operation modes: charge mode,
discharge mode, and high-impedance (HZ) mode.
In Top Off mode, when charges current decreases
to 10% of set fast charge current, the boost
converter goes into end of charge mode and keep
monitoring the battery voltage.
High Impedance (HZ) Mode
HZ mode is the default mode. In HZ mode, all the
switches are turned off , only PB circuit alive and
the IC draws less than 10uA current from VBAT.
Recharge
In EOC, device would re-charge batteries when
both battery voltage levels drops 5% below VEOC
.
Discharge Mode
In discharge mode, Buck converter operates in CV/
CC regulation. VOUT1 current limit is set at 1.25A
and VOUT2 current limit is set at 2.65A.
Battery Removal
If the battery is removed, boost converter regulates
at the programmed regulation voltage.
Charge Mode
Cell Balance
ACT2804 is configured in charge mode (boost
mode) when VIN is valid. In this mode, a battery is
charged with trickle, preconditioning, fast charge,
top-off and end of charge (EOC). The typical
charge management is shown in Figure 1.
Cell Balance is activated in both Fast Charge and
Top Off modes. Each battery is connected with a
parallel bleeding switch.
Push Button
PB is always watched in HZ mode and discharge
mode. If the push but on PB is pressed for >40mS
in HZ mode, the LED (s) will turn on for 5 seconds.
In the mean time, discharge mode is enabled.
Precondition Charge
When operating in precondition state, the cell is
charged at a reduced current at 15% of the
programmed maximum fast charge constant
current. Once VBAT reaches the precondition
threshold voltage the state machine jumps to the
fast charge state.
Fast Charge
If battery voltage is above preconditioning
threshold, boost converter charges battery with
constant current. In fast charge state, the ACT2804
VEOC
RECHARGE
FAST CHARGEB CURRENT
Current
A: PRECONDITION STATE
Voltage
B: FAST-CHARGE STATE
C: TOP-OFF STATE
VPRECHARGE
D: END-OF-CHARGE STATE
END-OF-CHARGE CURRENT
PRECONDITION CHARGE CURRENT
STATE
A
B
C
D
B
Figure 1. Typical Li+ Charge Profile and ACT2804 Charge States
Innovative PowerTM
- 10 -
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