LP28400 Datasheet, PDF (14/17 Pages) Lowpower Semiconductor inc – Programmable Charge Current Up to 3000mA

Preliminary Datasheet
LP28400
Operation Application
The LP28400 is a constant current, constant voltage 1-cell and
2-cell Li-Ion battery charger controller that uses a current mode
PWM step-down (buck) switching architecture. The charge
current is set by an external sense resistor across the SRP and
SRN pins. Voltage amplifier and the resistor divider provide
regulation with ±1% accuracy.
Normal Charge Cycle
The LP28400 series offers a high accuracy voltage regulator on
for the charging voltage. The LP28400 uses CELL pin to select
number of cells with a fixed 4.2V/cell. Connecting CELL to
AGND or floating CELL sets 2 cell output, and connecting to
VREF sets 1 cell output
CELL PIN
GND or Floating
VREF
VOLTAGE ULATION
8.4V
4.2V
Normal Charge Cycle
A charge cycle begins when the voltage at the V_CC pin rises
above the UVLO threshold level and when a battery is
connected to the charger output. If the BAT pin is less than
2.9V/5.8V, the charger enters trickle charge mode. In this mode,
the LP28400 supplies approximately 1/10 the ISET rammed
charge current to bring the battery voltage up to a safe level for
full current charging.
When the BAT pin voltage rises above 2.9V/5.8V, the charger
goes into the full- scale constant current charge mode. In
constant current mode The charge current is set by an external
sense resistor across the SRP and SRN charge current is
supplied to the battery. When the BAT pin approaches the final
float voltage (4.2V/8.4V), LP28400 enters constant-voltage
mode and the charge current begins to decrease. When the
charge current drops to 1/10 of the ISET rammed value, the
charge cycle ends.
Charge Current Regulation
The ISET input sets the maximum charging current. Battery
current is sensed by current sensing resistor RSR connected
between SRP and SRN. The full-scale differential voltage
between SRP and SRN is 75mV max.
Under high ambient temperature, the charge current will fold
back to keep IC temperature not exceeding 125°C
Input Current Regulation
The total input current from an AC adapter or other DC sources
is a function of the system supply current and the battery
charging current. System current normally fluctuated as
portions of the systems are powered up or down. Without
Dynamic Power Management (DPM), the source must be able
to supply the maximum system current and the maximum
available charger input current simultaneously. By using DPM,
the input current regulator reduces the charging current when
the summation of system power and charge power exceeds the
maximum input power. Therefore, the current capability of the
AC adapter can be lowered, reducing system cost., the sense
voltage between ACP and ACN is 75mV typ.
The ACP and ACN pins are used to sense across RAC with
default value of 20mΩ. However, resistors of other values can
also be used. A larger sense resistor will give a larger sense
voltage and higher regulation accuracy, at the expense of
higher conduction loss.
Charge Termination
A charge cycle is terminated when the charge current falls to
1/10th the SRP and SRN rammed value after the final float
voltage is reached. This condition is detected by using an
internal, filtered comparator to monitor the SRP and SEN pin.
When the SRP and SEN pin voltage falls below 1/10 for longer
than TTERM_DEG, charging is terminated. The charge current
is latched off and the LP28400 enters standby mode, where the
input supply current drops to 1.2mA. (Note: C/10 termination is
disabled in trickle charging and thermal limiting modes).
When charging, transient loads on the VSRP-SRN can cause
the VSRP-SRN to fall below 1/10 for short periods of time
before the DC charge current has dropped to 1/10th the
VSRP-SRN rammed value. The 100ms filter time
(TTERM_DEG) on the termination comparator ensures that
transient loads of this nature do not result in premature charge
cycle termination. Once the average charge current drops
LP28400-00 Version 1.0 May.-2013 Email: [e-mail] www.lowpowersemi.com Page 14 of 17