LP28400 Datasheet, PDF (15/17 Pages) Lowpower Semiconductor inc – Programmable Charge Current Up to 3000mA

Preliminary Datasheet
LP28400
below 1/10th the VSRP-SRN rammed value, the LP28400
terminates the charge cycle and ceases to provide any current
through the BAT pin. In this state, all loads on the BAT pin must
be supplied by the battery.
to VTCO thresholds. The controller suspends charge by turning
off the PWM charge MOSFETs.
Charge Status Indicator (STAT)
The open-drain STAT output indicate various charger
operations as shown in the following table. these status pins
can be used to driver LEDs or communicate to the host
processor. Note that OFF indicates the open-drain transistor is
turned off. A microprocessor can be used to distinguish
between these three states—this method is discussed in the
Applications Information section.
Charge STATE
Charging
Charge done
STAT
ON
OFF
Safety Timers
As a safety backup, the charger also provides an internal fixed
35 minutes pre-charge safety timer and an internal fixed 7 hours
fast charge timer
Assuming a NTC thermistor on the battery pack have
resistance at 0°C and 45°C are RTHCOLD and RTHHOT,
the values of RT1 and RT2 can be determined by using below
equations
Soft-Start Charger Current
The charger automatically soft-starts the charger regulation
current every time the charger goes into fast-charge to ensure
there is no overshoot or stress on the output capacitors or the
power converter. The soft-start consists of stepping-up the
charge regulation current into 8 evenly divided steps up to the
programmed charge current. Each step lasts around 1.4ms, for
a typical rise time of 11.2ms. No external components are
needed for this function.
Battery Temperature Detection
The controller continuously monitors battery temperature by
measuring the voltage between the TS pin and AGND. A
negative temperature coefficient resistance (NTC) and an
external voltage divider typically develop this voltage. The
controller compares this voltage against its internal thresholds
to determine if charging is allowed. To initiate a charge cycle,
the battery temperature must be within the VLTF to VHTF
thresholds. If battery temperature is outside of this range, the
controller suspends charge and waits until the battery
temperature is within the VLTF to VHTF range. During the
charge cycle the battery temperature must be within the VLTF
Temperature Sensing Configuration
VREF
LP28400
TS
RTC1
RT2
NTC
System Power Selector
The IC automatically switches adapter or battery power to the
system load. The battery is connected to the system by default
during power up or during SLEEP mode. When the adapter
LP28400-00 Version 1.0 May.-2013 Email: [e-mail] www.lowpowersemi.com Page 15 of 17