LP3947 Datasheet, PDF (10/14 Pages) National Semiconductor (TI) – USB/AC Adaptor, Single Cell Li-Ion Battery Charger IC

Application Notes (Continued)
TABLE 2. LED Indicator Summary
Charger Off
Charging Li Ion Battery*
Maintenance Mode
Charging Li Ion Battery after Passing Maintenance Mode
EN Pin = LOW
LDO Mode
5.6 Hr Safety Timer Flag/Battery Temperature Violation
* Charging Li Ion battery for the first time after V_CHG-IN insertion.
RED LED
(CHG)
OFF
ON
OFF
OFF
OFF
OFF
ON
GREEN LED
(EOC)
OFF
OFF
ON
ON
ON
OFF
ON
Ts PIN
The LP3947 continuously monitors the battery temperature
by measuring the voltage between the Ts pin and ground.
Charging stops if the battery temperature is outside the
permitted temperature range set by the battery’s internal
thermistor R_T and the external bias resistor R_S. A 1% preci-
sion resistor should be used for R_S. A curve 2 type thermistor
is recommended for R_T. The voltage across R_T is propor-
tional to the battery temperature. If the battery temperature is
outside of the range during the charge cycle, the LP3947 will
suspend charging. As an example, for a temperature range
of 0˚C to 50˚C, a 10kΩ for the thermistor and a 4.1kΩ for R_s
should be used. When battery temperature returns to the
permitted range, charging resumes from the beginning of the
flow chart and the 5.6 hr safety timer is reset. Refer to Figure
3. LP3947 Charger Flow Chart for more information.
In absence of the thermistor, Ts pin will be pulled high to VT
and the LP3947 goes into LDO mode. In this mode, the
internal power FET provides up to 1.2 amp of current at the
BATT pin. The LDO output is set to 4.1V or 4.2V, depending
on the programmed battery regulation voltage. When oper-
ating at higher output currents, care must be taken not to
exceed the package power dissipation rating. See “Thermal
Performance of LLP Package” section for more detail.
Voltage on the Ts Pin
2.427v ≤ Ts < 2.7V
0V ≤ Ts ≤ 1.39V
1.39V < Ts < 2.427V
Charger Status
Charger Off
Charger On
LDO MODE
The charger is in the LDO mode when the Ts pin is left
floating. This mode of operation is used primarily during
system level testing of the handset to eliminate the need for
battery insertion. CAUTION: battery may be damaged if
device is operating in LDO mode with battery connected.
The internal power FET provides up to 1.2 amp of current at
BATT pin in this mode. The LDO output is set to 4.1V. When
operating at higher output currents, care must be taken not
to exceed the package power dissipation rating. See “Ther-
mal Performance of LLP Package” section for more detail.
EN PIN
The Enable pin is used to enable/disable the charger, in both
the charger mode and the LDO mode, see Figures 5, 6. The
enable pin is internally pulled HIGH to the CHG-IN pin. When
the charger is disabled, it draws less than 4 µA of current.
Charger Status in Relation to Ts Voltage
Voltage on the Ts Pin
Ts ≥ 2.7V
Charger Status
LDO Mode
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