LP28300 datasheet(7/10 Pages) POWER

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Preliminary Datasheet

LP28300

LP28300 – 01 Version

1.1 Datasheet

Sep.-2010

www.lowpowersemi.com

Page 7 of 10

Operation

The LP28300 is a constant current, constant voltage

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 (RSENSE) across the SENSE and BAT

pins. The final battery float voltage is internally set

to 4.2V per cell. For batteries like lithium-ion that

require accurate final float voltage, the internal 2.4V

reference, voltage amplifier and the resistor divider

provide regulation with ±1% accuracy.

Figure 1.Typical Charge Profile

A charge cycle begins when the voltage at the VCC

pin rises above the UVLO level and is 250mV or

more greater than the battery voltage. At the

beginning of the charge cycle, if the battery voltage

is less than the trickle charge threshold, 2.9V for the

4.2 version, the charger goes into trickle charge

mode. The trickle charge current is internally set to

15% of the full-scale current. If the battery voltage

stays low for 30 minutes, the battery is considered

faulty and the charge cycle is terminated. When the

battery voltage exceeds the trickle charge threshold,

the charger goes into the full-scale constant current

charge mode. In constant current mode, the charge

current is set by the external sense resistor RSENSE

and an internal 100mV reference;

When

the

battery

voltage

approaches

the

programmed float voltage, the charge current will

start to decrease. When the current drops to 25%

of the full-scale charge current, an internal

comparator turns off the internal pull-down

N-channel MOSFET at the STAT pin, and connects

a weak current source to ground to indicate a near

end-of-charge condition. A 10kΩ NTC (negative

temperature

coefficient)

thermistor

can

connected from the NTC pin to ground for battery

temperature qualification. The charge cycle is

suspended when the temperature is outside of the

0°C to 50°C window.

Shutdown

The LP28300 can be shut down by pulling the

COMP pin to ground which pulls the GATE pin

high turning off the external P-channel MOSFET.

When the COMP pin is released, the internal timer

is reset and a new charge cycle starts. In shutdown,

the output of the CHRG pin is high impedance and

the quiescent current remains at 1.5mA. Removing

the input power supply will put the charger into

sleep mode. If the voltage at the VCC pin drops

below (VBAT + 250mV) or below the UVLO level,

the LP28300 goes into a low current (ICC = 10µA)

sleep mode, reducing the battery drain current.

Automatic Recharge

Once the charge cycle is terminated, the LP28300

continuously monitors the voltage on the BAT pin

using a comparator with a 2ms filter time

RECHARGE). A charge cycle restarts when the battery

voltage falls below 4.05V (which corresponds to

approximately 80% to 90% battery capacity). This

ensures that the battery is kept at or near a fully

charged condition and eliminates the need for

periodic charge cycle initiations. STAT output enters

a strong pull-down state during recharge cycles.

Battery Temperature Detection

negative

temperature

coefficient

(NTC)

thermistor located close to the battery pack can be

used to monitor battery temperature and will not

allow charging unless the battery temperature is

within an acceptable range. Connect a 10kΩ

thermistor from the TS pin to ground. If the

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