LX2202

Microsemi

Integrated Products Division

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

Page 9

Copyright

© 2004

Rev. 1.0a, 2006-02-09

2A Li-Ion Linear Charger and Power Control

TM

®

TH EORY OF O PERAT ION

The LX2202 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 LX2202 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 LX2202 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 LX2202 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 LX2202 enters a Voltage

Monitoring mode. In this mode the LX2202 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 LX2202 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 LX2202 senses the

current flowing from the USB terminal to the VDD

terminal; then it limits the USB current by reducing the

VID0 is used to enable discharge mode enable.

The

system load is connected to VDD. The input power is

connected to VDD through an external diode. When the

input power is removed, the battery current flows from

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 LX2202 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

UNDER VOLTAGE LOCK OUT

The LX2202 has an under voltage lock-out feature that

monitors the VDD terminal and prevents the battery

charger from entering charge mode if the VDD terminal is

less than 3.6V (nominal).