LX2208ILD データシートの表示（PDF） - Microsemi Corporation

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LX2208ILD

2 Amp Three Level Lithium Ion Battery Charger

Microsemi Corporation 

LX2208

2 Amp Three Level Lithium Ion Battery Charger

®

TM

PRODUCTION DATA SHEET

THEORY OF OPERATION

GENERAL DESCRIPTION

The LX2208 charges a single cell Lithium Ion or

Lithium Polymer battery using two steps: a constant

current mode followed by a constant voltage mode. The

maximum charging current during the Constant Current

Mode of the charging profile can be logically set (using

H/ L pin) to two resistor-programmable levels. The

resistor RHCP connected between HCP and GND pin sets

the higher level current. The resistor RLCP connected

between LCP and GND pin sets the lower level current.

There is also a 20% logic input that selects either the full

current set by the LCP resistor RLCP or 20% of that value.

The charger will terminate constant voltage charging once

the current drops below the taper current setting which is

10% of the high charge current setting (determined by

HCP resistor RHCP value).

CONDITIONING CURRENT CHARGE MODE

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 HCP programmable constant current

level. Once the battery terminal voltage exceeds the

conditioning current threshold, the full constant current

level is applied (unless charging current is limited by one

of the other charger control loops).

CHARGE TERMINATION MODE

To increase system battery life and avoid float charging,

the LX2208 disconnects the charger once the battery has

been fully charged. The charge termination state occurs at

the end of constant voltage mode. The termination current

is set by the value of the resistor RHCP connected between

HCP pin and GND. The STAT pin changes state when

charging is completed.

TOP OFF CHARGE MODE

Once the charger has completed a charge cycle, if power

remains applied, the LX2208 enters a Voltage Monitoring

mode. In this mode, the LX2208 monitors the battery

terminal voltage and applies a top off charge if the battery

voltage drops below the top off threshold.

ADAPTER OR USB SELECTION

The LX2208 supports battery charging from a system

that provides adapter power or USB power using the same

external connector. Figure 1 shows one example of a

system using a special USB adapter cable to determine

whether the power source is USB or Wall Adapter.

Similarly, if the system processor senses the absence of

USB data, it can logically set the H/ L logic level high to

allow a higher charge current to be used.

INPUT SUPPLY QUALIFICATION

If the input supply is not high enough for the internal

4.2V reference to operate, charge termination will be

prevented. This may be useful if supply is severely current

limited.

USB CHARGE MODE AND CURRENT LIMIT

The LX2208 is fully compliant with, and supports, the

USB specifications – the Low Power Peripheral (100mA)

and High Power Peripherals (500mA). USB current levels

can be set using the appropriate values of the LCP

programming resistor RLCP. 20% logic input selects USB

high/low charge current. When the SD pin is pulled high,

the USB input enters Shut Down mode and will not present

a load to the IN pin.

DC OK

The IN input is monitored and DC OK is set to a logic

low to report the presence of the power source with

sufficient voltage to charge the battery. The DC OK

threshold is the larger of the UVLO threshold or the battery

voltage.

PROTECTION FEATURES

Conditioning Current Mode – If the battery terminal

voltage is less than 2.7V, the battery charger will reduce the

charge current to 5%. This also protects the appliance from

overheating by trying to drive the full charging current into a

short circuited battery.

Under Voltage Lockout – The charge cycle will not start

until the IN voltage rises above 3.1V. Hysteresis helps

alleviate chattering on and off.

Thermal Control Loop – If the power dissipation of the

charger becomes excessive, the charge current will be

linearly reduced to prevent the die temperature from getting

above 140°C. This does not cause the charge cycle to stop.

Reverse Current Blocking – If IN input is grounded,

current will not flow from the BAT pin through the charger.

No external blocking diode is required on the input.

Shut Down Mode – If the SD pin is asserted a logic high,

the charger enters a shut down mode where a very low

quiescent current prevents drain from the battery.

Copyright © 2007

Rev. 1.0, 2007-04-03

Microsemi

Analog Mixed Signal Group

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

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