BQ24745_14 Datasheet, PDF (21/39 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery

www.ti.com
bq24745
SLUS761D – DECEMBER 2007 – REVISED OCTOBER 2011
Table 3. Charge Voltage Register (0x15) (continued)
BIT
BIT NAME
11
Charge voltage, DACV 7
12
Charge voltage, DACV 8
13
Charge voltage, DACV 9
14
Charge voltage, DACV 10
15
–
DESCRIPTION
0 = Adds 0 mV of charger voltage
1 = Adds 2,048 mV of charger voltage
0 = Adds 0 mV of charger voltage
1 = Adds 4,096 mV of charger voltage
0 = Adds 0 mV of charger voltage
1 = Adds 8,192 mV of charger voltage
0 = Adds 0 mV of charger voltage
1 = Adds 16,384 mV of charger voltage
Not used
CHARGE CURRENT REGULATION
The ChargeCurrent() SMBus 6-bit DAC register sets the maximum charging current. Battery current is sensed by
resistor R_SR connected between the CSOP and CSON pins. The maximum full-scale differential voltage between
CSOP and CSON is 80.64 mV. Thus, for a 0.010-Ω sense resistor, the maximum charging current is 8.064 A.
The CSOP and CSON pins are used to measure the voltage across R_SR, which has a default value of 10 mΩ.
However, resistors of other values can also be used. A larger sense resistor results in a larger sense voltage and
higher regulation accuracy, but at the expense of higher conduction loss.
To set the charge current, use the SMBus to write a 16-bit ChargeCurrent() command using the data format
listed in Table 4. The ChargeCurrent() command uses the Write-Word protocol (see Figure 33). The command
code for ChargeCurrent() is 0x14 (0b0001 0100). When using a 10-mΩ sense resistor, the bq24745 provides a
charge current range of 128 mA to 8.064 A, with 128-mA resolution. Set ChargeCurrent() to 0 to terminate
charging. Setting ChargeCurrent() below 128 mA, or above 8.064 A, clears DAC and terminates charge.
The bq24745 includes a foldback current limit when the battery voltage is low. If the battery voltage is less than
3.6 V but above 2.5 V, any charge current limit above 3 A is clamped at 3 A. If the battery voltage is less than
2.5 V, the charge current is set to 220 mA until that voltage rises above 2.7 V. The ChargeCurrent() register is
preserved and becomes active again when the battery voltage is higher than 2.7 V. This function effectively
provides a fold-back current limit, which protects the charger during short circuit and overload.
On reset, the ChargeVoltage() and ChargeCurrent() values are cleared (0) and the charger remains off until both
the ChargeVoltage() and the ChargeCurrent() commands are sent. During reset, both high-side and low-side
FETs remain off until the charger is started.
Table 4. Charge Current Register (0x14), Using 10-mΩ Sense Resistor
BIT
BIT NAME
0
–
1
–
2
–
3
–
4
–
5
–
6
–
7
Charge current, DACI 0
8
Charge current, DACI 1
9
Charge current, DACI 2
10
Charge current, DACI 3
11
Charge current, DACI 4
DESCRIPTION
Not used
Not used
Not used
Not used
Not used
Not used
Not used
0 = Adds 0 mA of charger current
1 = Adds 128 mA of charger current
0 = Adds 0 mA of charger current
1 = Adds 256 mA of charger current
0 = Adds 0 mA of charger current
1 = Adds 512 mA of charger current
0 = Adds 0 mA of charger current
1 = Adds 1,024 mA of charger current
0 = Adds 0 mA of charger current
1 = Adds 2,048 mA of charger current
Copyright © 2007–2011, Texas Instruments Incorporated
Product Folder Link(s) :bq24745
Submit Documentation Feedback
21