ACT2823
REV 1, 01-DEC-2016
GENERAL INFORMATION
ACT2823 is
discharging
a
complete battery charging and
programmed fast charge current. This prevents damage
to a heavily discharged battery. When the battery
voltage increases above the precondition threshold, the
charger transitions to Fast Charge mode. The battery
voltage is measured between the BATP and BATN pins.
power management solution for
applications of duel-cell, lithium-based backup battery
pack or power bank. With a USB input, the ACT2823
charges a dual cell Li-Ion battery and provides power to
the output. When USB power is removed, it powers the
output from the battery. The ACT2823 contains a fully
integrated, advanced, bidirectional, synchronous
boost/buck converter. The converter automatically
configures itself as a boost or a buck, depending on the
system level conditions. No microprocessor or user
intervention is needed to switch between operating
modes.
Fast Charge
When the battery voltage is above precondition
threshold, the charger operates in Fast Charge mode.
Fast Charge mode charges the battery with a constant
current set to the programmed fast charge current. The
fast charge current is set by the resistor on the ICST pin.
The charger stays in Fast Charge mode until the battery
voltage reaches the End-of-Charge Voltage, typically
8.4V or 8.7V.
ACT2823 operates in three modes: charge mode,
discharge mode, and high-impedance (HZ) mode. It
operates in charge mode when an input voltage is
present. It operates in discharge mode when the input
source is not present. It also contains a High Impedance
(HZ) Mode to minimize standby power when input
power is not present and a load is not connected.
Figure 3 shows a block diagram with current sensing.
Io
Output
Iin
VOUT
SW
Input
VIN
L
Cout1
Cin
TheACT2823 automatically prioritizes power to the load.
If the input voltage drops due to a weak input source,
the charger reduces charging current to ensure the load
can continue to operate.
ACT2823
RCS
Ic
ICST
BAT
RICST
BATP
Battery1
Battery2
BATN
FEATURES
Charger
Figure 3: Battery Current Monitoring
The ACT2823 charger contains a boost converter that
charges a dual Li-Ion battery from a USB input. If a
battery is connected, charging is accomplished with a
fully integrated boost converter and consists of five
phases: trickle charge, preconditioning, fast charge, top
off, and end of charge. It contains full, built in charging
protection, including over-charge protection, over
discharge protection, thermal regulation, and automatic
power path priority to the load.
The following equation calculates the fast charge
current, Ic.
200
Ic(A)
(1)
R
CS * RICST
Where RCS is the current sense resistor in mΩand
RICSTis the fast charge current setting resistor in kΩ. As
an example, setting RCS=25mΩ and RICST=8kΩ results
in a 1A fast charge current. Always design for a current
sense resistor voltage between 20mV-75mV in fast
charge mode.
Trickle Charge
When the battery is over-discharged, it must be charged
with a very small current to prevent battery damage.
The ACT2823 provides this protection by charging the
battery with 40mA directly from VIN when the battery
voltage is lower than 96% of VIN. When the battery
voltage increases to greater than 96% of VIN, the
charger transitions to Precondition Charge mode. Note
that Q1 is turned off and VOUT is not present in Trickle
Charge mode.
During discharge mode, the IC inverts the inputs to the
battery current sense amp and the voltage on ICST can
be used to measure the discharge current. The
following equation calculates the discharge current.
20 VICST
RICST
IDISCHARGE
(2)
Precondition Charge
Where VICST is the voltage on the ICST pin in volts, RICST
is the fast charge current setting resistor in kΩ, and
IDISCHARGE is the battery discharge current in amps. As
an example, measuring VICST=0.4V with RICST=8kΩ
indicates 1A discharge current.
When the battery voltage is below the precondition
threshold, typically 5.6V, the charger operates in
Precondition mode. In this mode, it charges the battery
with a constant current that is set to 15% of the
Innovative PowerTM
ActiveSwitcherTM is a trademark of Active-Semi.
12
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
