Datasheet

1 PF
1k
EN
ISEL
Mode
SCL
SDA
T
S
V
T
R
S
R
T
VB
Sense
BATT
10 PF
Li-Ion
CHG
EOC
GND
CHG-IN
LP3947
Wall
Adaptor
To
System
Supply
USB
Port
P-Ch
MOSFET
Diff-Amp
10k
LP3947
www.ti.com SNVS298B –NOVEMBER 2004–REVISED APRIL 2013
APPLICATION NOTES
LP3947 CHARGER OPERATION
The LP3947 charge cycle is initiated with AC adaptor or USB power source insertion. If the voltage on the CHG-
IN pin meets under-voltage (V
UVLO-TSHD
), over-voltage (V
OVLO-TSHD
) requirements, and the Adaptor OK signal is
detected, then pre-qualification cycle begins (see Figure 2). In this cycle, a safe current level, less than 70mA, is
pumped into the battery while the voltage across the battery terminals is measured. Once this voltage exceeds
3.0V, the controller will initiate constant current fast charge cycle. If the CHG-IN pin is connected to an AC
adaptor, the default charge current is 500 mA and I
2
C interface can be used to program this parameter. If the
CHG-IN pin is connected to the USB port, constant current cycle will start with a default of 100 mA. During this
cycle, the 5.6 hr safety timer starts counting.
If the 5.6 hr safety timers times out during constant current cycle, charging is terminated. As the battery is
charged during constant current mode, the voltage across pack terminal increases until it reaches 4.2V (or 4.1V).
As soon as pack terminal reaches 4.2V (or 4.1V), the controller starts operating in constant voltage mode by
applying regulated V
BATT
voltage across the battery terminals. During this cycle, the charge current, I
CHG
,
continues to decrease with time and when it drops below 0.1C (default value), the EOC signal is activated
indicating successful completion of the charge cycle. The EOC current can be programmed to 0.1C, 0.15C, or
0.2C. The default value is 0.1C. After completing the full charge cycle, the controller will start the maintenance
cycle where battery pack voltage is monitored continuously. During the maintenance cycle, if the pack voltage
drops 200 mV below the termination voltage, charge cycle will be initiated providing that the wall adaptor is
plugged in and is alive.
Charging terminates when the battery temperature is out of range. For more explanation, please refer to Ts PIN.
The LP3947 with I
2
C interface allows maximum flexibility in selecting the charge current, battery regulation
voltage and EOC current. The LP3947 operates in default mode during power up. See I
2
C INTERFACE for more
detail.
When charging source comes from the USB port, charging starts with 100 mA (low power mode, ISEL = high).
The USB controller can set the ISEL pin low to charge the battery at 500 mA. A simple external circuit selects
between an AC adaptor or the USB port. The circuit is designed with priority given to the AC adaptor.
Figure 3. LP3947 with External Switch
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Product Folder Links: LP3947