LP3947ISD-51 Datasheet, PDF (9/20 Pages) Texas Instruments – LP3947 USB/AC Adaptor, Single Cell Li-Ion Battery Charger IC

LP3947
www.ti.com
SNVS298B – NOVEMBER 2004 – REVISED APRIL 2013
CHARGE CURRENT SELECTION IN CONSTANT CURRENT MODE
In the AC adaptor mode, the LP3947 is designed to provide a charge current ranging from 100 mA to 750 mA, in
steps of 50 mA, to support batteries with different capacity ratings. The default value is 500 mA. No external
resistor is required to set the charge current in the LP3947. In the USB mode, the LP3947 will initially charge
with 100 mA (ISEL = high). By setting the ISEL pin low, charge current can be programmed to 500 mA. In
addition, with ISEL = low, the charge current can be programmed to different values via the I²C interface.
AC Adaptor Mode
USB Mode
Table 2. Charge Current Selection in AC Adaptor/USB Mode
MODE Pin
HIGH
HIGH
LOW
LOW
ISEL Pin
HIGH
LOW
HIGH
LOW
Functions
ISEL polarity is irrelevant. Default 500 mA charge current. Can be reprogrammed via
I²C.
100 mA charge current
Default 500 mA charge current. Can be reprogrammed via I²C.
BATTERY VOLTAGE SELECTION
The battery voltage regulation can be set to 4.1V or 4.2V by default. Please refer to Ordering Information for
more details.
END OF CHARGE (EOC) CURRENT SELECTION
The EOC thresholds can be programmed to 0.1C, 0.15C or 0.2C in the LP3947. The default value is 0.1C, which
provides the highest energy storage, but at the expense of longer charging time. On the other hand, 0.2C takes
the least amount of charging time, but yields the least energy storage.
CHARGE CURRENT SENSE DIFFERENTIAL AMPLIFIER
The charge current is monitored across the internal 120 mΩ current sense resistor. The differential amplifier
provides the analog representation of the charge current. Charge current can be calculated using the following
equation:
(V_DIFF - 0.497)
I_CHG =
1.655
(1)
Where voltage at Diff Amp output (V_DIFF) is in volt, and charge current (I_CHG) is in amps.
CHG-IN
Batt
R_Sense
120 m:
1.74V
Diff-Amp
0.583V
50 mA
750 mA
Charge Current
Figure 5. Charge Current Monitoring Circuit (Diff-Amp)
Monitoring the Diff Amp output during constant voltage cycle can provide an accurate indication of the battery
charge status and time remaining to EOC. This feature is particularly useful during constant voltage mode. The
current sense circuit is operational in the LDO mode as well. It can be used to monitor the system current
consumption during testing.
LED CHARGE STATUS INDICATORS
The LP3947 is equipped with two open drain outputs to drive a green LED and a red LED. These two LEDs work
together in combinations to indicate charge status or fault conditions. Table 3 shows all the conditions.
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