BQ24765_15 Datasheet, PDF (21/37 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery Charger With Integrated Power MOSFETs

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BIT
12
13
14
15
bq24765
SLUS999 – NOVEMBER 2009
Table 3. Charge Voltage Register (0x15) (continued)
BIT NAME
Charge Voltage, DACV 8
Charge Voltage, DACV 9
Charge Voltage, DACV 10
–
DESCRIPTION
0 = Adds 0mV of charger voltage
1 = Adds 4096mV of charger voltage
0 = Adds 0mV of charger voltage
1 = Adds 8192mV of charger voltage
0 = Adds 0mV of charger voltage
1 = Adds 16384mV of charger voltage
Not used
BATTERY CURRENT REGULATION
The Charge Current SMBus 6 bit DAC register sets the maximum charging current. Battery current is sensed by
resistor RSR connected between CSOP and CSON. The maximum full-scale differential voltage between CSOP
and CSON is 80.64mV. Thus, for a 0.010Ω sense resistor, the maximum charging current is 8.064A.
The CSOP and CSON pins are used to sense across RSR 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.
To set the charge current, use the SMBus to write a 16bit ChargeCurrent() command using the data format listed
in . The ChargeCurrent() command uses the Write-Word protocol (see Figure 28). The command code for
ChargeCurrent() is 0x14 (0b00010100). When using a 10mΩ sense resistor, the bq24765 provides a charge
current range of 128mA to 8.064A, with 128mA resolution. Set ChargeCurrent() to 0 to terminate charging.
Setting ChargeCurrent() below 128mA, or above 8.064A clears DAC and terminates charge
As charging goes on, the power loss on the switching fets causes the junction temperature to rise. The bq24765
provides a thermal regulation loop to throttle back the maximum charge current when the maximum junction
temperature limit is reached. Once the device junction temperature exceeds thermal regulation limit (typical
120°C), the thermal regulator reduces the charging current to keep the junction temperature at 120°C. When the
junction temperature rises to 125°C, the charging current decreases down close to 0A.
The bq24765 includes a foldback current limit when the battery voltage is low. If the battery voltage is less than
3.6V but above 2.5V, any charge current limit above 3A will be clamped at 3A. If the battery voltage is less than
2.5V, the charge current is set to 220mA until that voltage rises above 2.7V. The ChargeCurrent() register is
preserved and becomes active again when the battery voltage is higher than 2.7V. This function effectively
provides a fold-back current limit, which protects the charger during short circuit and overload.
Upon reset, the ChargeVoltage() and ChargeCurrent() values are cleared (0) and the charger remains off until
both the ChargeVoltage() and the ChargeCurrent() command are sent. During reset, both high side and low side
fets remain off until the charger gets started.
Table 4. Charge Current Register (0x14), 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, DACI 0
0 = Adds 0mA of charger current
1 = Adds 128mA of charger current.
8
Charge Current, DACI 1
0 = Adds 0mA of charger current
1 = Adds 256mA of charger current.
9
Charge Current, DACI 2
0 = Adds 0mA of charger current
1 = Adds 512mA of charger current.
10
Charge Current, DACI 3
0 = Adds 0mA of charger current
1 = Adds 1024mA of charger current.
Copyright © 2009, Texas Instruments Incorporated
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