BQ24765 Datasheet, PDF (22/36 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery Charger With Integrated Power MOSFETs

bq24765
SLUS999 – NOVEMBER 2009
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Table 4. Charge Current Register (0x14), Using 10mΩ Sense Resistor (continued)
BIT
BIT NAME
DESCRIPTION
11
Charge Current, DACI 4
0 = Adds 0mA of charger current
1 = Adds 2048mA of charger current.
0 = Adds 0mA of charger current
12
Charge Current, DACI 5
1 = Adds 4096mA of charger current, (Maximum charge current
8064mA.)
13
–
Not used
14
–
Not used
15
–
Not used
INPUT ADAPTER CURRENT REGULATION
The total Input Current from an AC adapter or other DC sources is a function of the system supply current and
the battery charging current. System current normally fluctuates as portions of the system are powered up or
down. Without Dynamic Power Management (DPM), the source must be able to supply the maximum system
current and the maximum charger input current simultaneously. By using DPM, the input current regulator
reduces the charging current to keep the input current from exceeding the limit set by the Input Current SMBus 6
bit DAC register. With the high accuracy limiting, the current capability of the AC adaptor can be lowered,
reducing system cost.
The CSSP and CSSN pins are used to sense R_AC with default value of 10mΩ. However, resistors of other values
can also be used. For a larger the sense resistor, you get a larger sense voltage, and a higher regulation
accuracy; but, at the expense of higher conduction loss.
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 bq24765
decreases the charge current to provide priority to system load current. As the system supply rises, the available
charge current drops linearly to zero.
where η is the efficiency of the DC-DC converter (typically 85% to 95%).
ƪ ƫ I_INPUT + I_LOAD )
I_LOAD V_BATTERY
V_IN h
) I_BIAS
(1)
To set the input current limit, use the SMBus to write a 16-bit InputCurrent() command using the data format
listed in Table 5. The InputCurrent() command uses the Write-Word protocol (see Figure 28). The command
code for InputCurrent() is 0x3F (0b00111111). When using a 10mΩ sense resistor, the bq24765 provides an
input-current limit range of 256mA to 11.004A, with 256mA resolution. InputCurrent() settings from 1mA to
256mA clears DAC and terminates charge. Upon reset the input current limit is 256mA.
Table 5. Input Current Register (0x3F), Using 10mΩ Sense Resistor
BIT
BIT NAME
DESCRIPTION
0
–
Not used
1
–
Not used
2
–
Not used
3
–
Not used
4
–
Not used
5
–
Not used
6
–
Not used
7
Charge Current, DACS 0
0 = Adds 0mA of charger current
1 = Adds 256mA of charger current.
8
Charge Current, DACS 1
0 = Adds 0mA of charger current
1 = Adds 512mA of charger current.
9
Charge Current, DACS 2
0 = Adds 0mA of charger current
1 = Adds 1024mA of charger current.
22
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