LX2201

Microsemi

Integrated Products Division

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 8

Copyright

© 2000

Rev. 1.2b, 2005-04-13

USB Li-Ion Battery Charger

TM

®

TH EORY OF O PERAT ION

The LX2201 is designed to charge a single cell Lithium

Ion battery using two steps: a constant current step

followed by a constant voltage step. The basic charger

function uses the VDD pins as an input and BAT pins as

the output. The LX2201 charger has a programmable

maximum current (programmable by the resistor value

between pin CCP to GND) which is the maximum

charging current during the Constant Current Mode of the

charging profile.

The low dropout of the pass element

allows the battery to be charged from a loosely regulated

power supply. In the Constant Voltage Mode, the battery

terminal voltage can be regulated to 4.1V or 4.2V by

strapping the VM pin to VDD or GND, respectively. The

charger will terminate constant voltage charging once the

current

drops

below

the

minimum

current

setting

(programmable by the resistor value between pin CTP to

GND).

The LX2201 has an integrated thermostat with a linear

thermal regulation loop that will throttle back the charging

current to prevent the internal die temperature from

exceeding 150ºC.

This feature prevents damage to the

system board when the IC exceeds its thermal temperature.

A conditioning current is applied to batteries that are

deeply discharged and have a terminal voltage less than

60% of the constant voltage level. The conditioning current

is 5% of the CCP programmable constant current level

(except where it might be limited in the USB states). Once

the battery terminal voltage exceeds the 60% level, the full

constant current level is applied (unless charging current is

limited by one of the other charger control loops).

To increase system battery life and avoid float charging,

the LX2201 turns off the pass element once the battery has

been fully charged. The charge termination state occurs at

the end of constant voltage mode. The charge status

changes state when charging is completed.

Once the charger has completed a charge cycle, if

power remains applied, the LX2201 enters a Voltage

Monitoring mode. In this mode the LX2201 monitors the

battery terminal voltage and applies a top off charge if the

battery voltage drops by more than 3% of full scale. This

feature is especially important for charging systems in

equipment where usage is infrequent.

The LX2201 is fully compliant with, and supports, the

USB specifications – the Low Power Peripheral (100mA)

and High Power Peripherals (500mA). VID1 logic input

selects USB charge currents.

The LX2201 senses the

current flowing from the VIN terminal to the VDD

terminal; then it limits the VIN current by reducing the

current

Note: the USB

Charge Limit circuit does not limit the input current and

only scales the charging current.

In discharge mode, VID0 is, indicate discharge mode

enable. The system load is connected to VDD. The input

power is connected to VDD through an internal diode.

When the input power is removed, the battery current

the LX2201 in a discharge mode configuration with both

AC adapter and USB inputs.

The USB input is diode

ORed to the VDD pin and uses a MOSFET to reduce the

diode drop across the ORing diode. The LX2201 provides

a signal “PSW” to control the MOSFET for charge and

discharge modes. When both AC and USB power are

applied the PSW signal is overridden by the AC adapter

diode and the MOSFET is turned off