Datasheet

BATTERY BATTERY
INPUT LOAD BIAS
IN
I V
I = I + + I
V η
é ù
´
ê ú
´
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bq24725A
SLUSAL0 –SEPTEMBER 2011 www.ti.com
The SRN pin is used to sense the battery voltage for voltage regulation and should be connected as close to the
battery as possible, and place a decoupling capacitor (0.1µF recommended) as close to the IC as possible to
decouple high frequency noise.
Table 5. Charge Voltage Register (0x15H)
BIT BIT NAME DESCRIPTION
0 - Not used.
1 - Not used.
2 - Not used.
3 - Not used.
4 Charge Voltage, DACV 0 0 = Adds 0mV of charger voltage.
1 = Adds 16mV of charger voltage.
5 Charge Voltage, DACV 1 0 = Adds 0mV of charger voltage.
1 = Adds 32mV of charger voltage.
6 Charge Voltage, DACV 2 0 = Adds 0mV of charger voltage.
1 = Adds 64mV of charger voltage.
7 Charge Voltage, DACV 3 0 = Adds 0mV of charger voltage.
1 = Adds 128mV of charger voltage.
8 Charge Voltage, DACV 4 0 = Adds 0mV of charger voltage.
1 = Adds 256mV of charger voltage.
9 Charge Voltage, DACV 5 0 = Adds 0mV of charger voltage.
1 = Adds 512mV of charger voltage.
10 Charge Voltage, DACV 6 0 = Adds 0mV of charger voltage.
1 = Adds 1024mV of charger voltage.
11 Charge Voltage, DACV 7 0 = Adds 0mV of charger voltage.
1 = Adds 2048mV of charger voltage.
12 Charge Voltage, DACV 8 0 = Adds 0mV of charger voltage.
1 = Adds 4096mV of charger voltage.
13 Charge Voltage, DACV 9 0 = Adds 0mV of charger voltage.
1 = Adds 8192mV of charger voltage.
14 Charge Voltage, DACV 10 0 = Adds 0mV of charger voltage.
1 = Adds 16384mV of charger voltage.
15 - Not used.
Setting Input Current
System current normally fluctuates as portions of the system are powered up or put to sleep. With the input
current limit, the output current requirement of the AC wall adapter can be lowered, reducing system cost.
The total input current, from a wall cube or other DC source, is the sum of the system supply current and the
current required by the charger. When the input current exceeds the set input current limit, the bq24725A
decreases the charge current to provide priority to system load current. As the system current rises, the available
charge current drops linearly to zero. Thereafter, all input current goes to system load and input current
increases.
During DPM regulation, the total input current is the sum of the device supply current I
BIAS
, the charger input
current, and the system load current I
LOAD
, and can be estimated as follows:
(2)
where η is the efficiency of the charger buck converter (typically 85% to 95%).
To set the input current limit, write a 16-bit InputCurrent() command (0x3FH or 0b00111111) using the data
format listed in Table 6. When using a 10mΩ sense resistor, the bq24725A provides an input-current limit range
of 128mA to 8.064A, with 128mA resolution. The suggested input current limit is set to no less than 512mA.
Sending InputCurrent() below 128mA or above 8.064A clears the register and terminates charging. Upon POR,
the default input current limit is 4096mA.
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