BQ24721 Datasheet, PDF (25/48 Pages) Texas Instruments – ADVANCED MULTI-CHEMISTRY AND MULTI-CELL SYNCHRONOUS SWITCH-MODE CHARGER AND SYSTEM POWER SELECTOR

bq24721
www.ti.com
ADDRESS
0x12
0x13
SLUS683 – NOVEMBER 2005
BLOCK DESCRIPTION (continued)
REGISTER
Charger mode
Charger status
DESCRIPTION
Used to set the charger operating modes.
Used to monitor the operating status of the charger.
The SMBus communications requires only two pins besides the analog ground pin—through the SDA (data) and
SCL (clock) pins. The open-drain SCL and SDA pins require pull-up resistors on the board pulling up to the host
digital output voltage rail. The pins can be pulled up to any rail between 3 V to 5 V.
An alarm is sent to the host through the ALARM open drain pin. This can be used to trigger an interrupt request
(IRQ). A low on the ALARM pin indicates there was a change on the Charger Status (0x13) register. The ALARM
pin stays low until the host reads the Charger Status (0x13) register, then the ALARM pin clears and returns to
the HI state. The open-drain ALARM pin requires a pull-up resistor that pulls up to the host digital input voltage
rail. The pin can be pulled up to any rail between 3 V to 5 V. The charge controller continues to operate whether
the host chooses to read or not to read the Charger Status (0x13) register. There is no communications
watchdog timer, so there is no need to continuously poll the Charger Status (0x13) register or have to
continuously reprogram any of the other registers.
Setting Charge Voltage (VBAT DAC register)
The charge voltage can be programmed by setting Charging Voltage(0x15) register. The SBS specification asks
for 16 bits to set the regulation voltage with a 1-mV LSB—giving a maximum possible voltage of 65.535 V. The
bq24721 uses bits 1 through 14 only, and maps them into the closest value of an internal 7-bit DAC on a per cell
basis using a 6.25-mV per cell LSB for three ranges: 9-V pre-charge voltage; 3 cells Li+ battery pack range; or 4
cells Li+ battery pack range. The 3 cell portion has an LSB of 18.75 mV and a range from 12 V-14.4 V; while the
4 cell portion has an LSB of 25 mV and a range from 16 V-19.2 V. Intermediate programmed voltages between
the internal 7-bit DAC values are truncated to the lower value to avoid an overvoltage on the battery.
Programmed voltages above 19.2 V are automatically set to the maximum 19.2-V limit. The charger is disabled
for programmed voltages below 12 V (except for 9 V), and for programmed voltages between 14.4 V – 16 V. This
triggers a voltage-out-of-range condition and the VOR bit of the Charger Status (0x13) register is set, and an
alarm (ALARM pin pulled low) is sent to the host. The default power-up-reset voltage value is 0 V, charger
disabled.
Setting Charge Current (IBAT DAC register)
The charge current can be programmed using the Charging Current (0x14) register. The SBS specification asks
for 16 bits to set the charge current with a 1-mA LSB—giving a maximum possible current of 65.535 A using a
10-mΩ sense resistor. The bq24721 uses bits 7 – 14 only to limit the range within a practical operating range.
The current range is 0 mA to 16.384 A with an LSB of 128 mA using a 10-mΩ sense resistor. The charger is
disabled when the programmed input current is 0 A. The default power-up-reset current value is 0 A, charger
disabled. Other sense resistors could be used to set the charge current—the user would just need to transform
the DAC current table values to the new current values by dividing the current by 10 mΩ, then multiplying by the
new sense resistor value used.
Setting Input (DPM) Current (IDPM DAC register)
The input current can be similarly programmed using the Input Current (0x3F) register. The SBS specification
asks for 16 bits to set the input current with a 1-mA LSB—giving a maximum possible current of 65.535 A using
a 10-mΩ sense resistor. The bq24721 uses bits 7 – 14 only to limit the range within a practical operating range.
The current range is 0 mA to 16.384 A with an LSB of 128 mA using a 10-mΩ sense resistor. The charger is
disabled when the programmed input current is 0 A. The default power-up-reset current value is 0 A, charger
disabled. Other sense resistors could be used to set the input current—the user would just need to transform the
DAC current table values to the new current values by dividing the current by 10 mΩ, then multiplying by the new
sense resistor value used.
25