LX2207
PRODUCTION DATA SHEET
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
Copyright © 2007
Rev. 1.0a, 2007-10-08
WWW.Microsemi .COM
Three Level Lithium Ion Battery Charger
TM
®
THEORY OF OPERATION
GENERAL DESCRIPTION
The LX2207 charges a single cell Lithium Ion 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) to two preprogrammed
levels set by resistors connected to HCP and LCP (High
and Low current). A 20% logic input selects either the full
current set by the LCP resistor 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 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 one of the other charger control loops limits
charging current).
CHARGE TERMINATION MODE
To increase system battery life and avoid float charging,
the LX2207 turns off the pass element once the battery is
fully charged. The charge termination state occurs at the
end of constant voltage mode. The value of the resistor
connected to the HCP programming pin sets the
termination current. The STAT pin changes state when
charge cycle has completed.
TOP OFF CHARGE MODE
Once the charger has completed a charge cycle, if power
remains applied, the LX2207 enters a Voltage Monitoring
mode. In this mode the LX2207 monitors the battery
terminal voltage and applies a top off charge if the battery
voltage drops below the top of threshold.
ADAPTER OR USB SELECTION
The LX2207 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 for
the wall adapter.
USB CHARGE MODE AND CURRENT LIMIT
The LX2207 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 for the LCP
programming resistor. 20% logic input selects USB
high/low charge currents. When the SD pin is pulled high,
the USB input enters Suspend mode and will not present a
load to the IN pin.
DCOK
The IN input is monitored and DCOK is set to a logic
low to report the presence of the power source with
sufficient voltage to charge the battery. The DCOK
threshold is the larger of the UVLO threshold or the battery
voltage.
P
ROTECTION 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 3.8V. Hysteresis helps
alleviate chattering on and off.
Thermal Control loop
– If the power dissipation of the
charger becomes excessive, the charge current will be
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.
Sleep Mode
– If the SD pin is a logic high, the charger
enters a sleep mode where a very low quiescent current
prevents drain from the battery.
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