BQ24721 Datasheet, PDF (24/48 Pages) Texas Instruments – ADVANCED MULTI-CHEMISTRY AND MULTI-CELL SYNCHRONOUS SWITCH-MODE CHARGER AND SYSTEM POWER SELECTOR

bq24721
SLUS683 – NOVEMBER 2005
www.ti.com
ADAPTER
POWER
external
SYSTEM & CHARGE POWER
SELECTOR
Chrg Dischrg
Vin Bat Chrg Dischrg
SYSTEM
bq24721
BATTERY
CHARGER
CONTROLLER
IC
&
CONVERTER
BATTERY
Primary
BATTERY
Secondary
PSID
I/O SMBus
SMBus
HOST - Embedded Controller (EC)
SMBus
I/O
Figure 57. Host Controller
BLOCK DESCRIPTION
Detail Block Diagram
The bq24721 charge controller can be used to charge Li-ion, NiMH, or NiCd batteries. The high efficiency
synchronous buck controller uses n-channel power MOSFETs for both the high-side control device and the
low-side synchronous device. The controller offers high regulation accuracy of the charge current, battery
voltage, and input current limits. The low offset of the current loops allow using sense resistors with low-value,
such as 10 mΩ.
An embedded controller host programs the battery voltage, charge current, and input current regulation limit
thresholds through an SMBus interface using SBS-like DAC registers. The embedded host can control the
operation of the charger through a Charge Control (0x12) register, and monitor the status of the charger through
a Charger Status (0x13) register.
The voltage loop regulates the battery voltage to the programmed value, and prevents the voltage from
exceeding that value when the battery is connected. The charge current loop regulates the battery charge current
to the programmed value, and prevents the charge current from exceeding that value. Through the use of
dynamic power management (DPM), the input current loop regulates the battery charge current to the
programmed value, and prevents the input current from exceeding that value. The three regulation loops operate
independently, yet only require a single loop compensation network.
The system power selector function selects the appropriate power source for the system load. If the adapter is
detected, then the adapter is connected to the system load. When the adapter is removed, the battery is selected
to power the system load. A battery learn cycle can be performed when the adapter is present by setting the
CONTROL(0x12) register into Learn Mode via SMBus by the embedded host. This disconnects the adapter from
the system; and instead, connect the battery to the system. This is typically done for Ni-based batteries.
SMBus Interface
The bq24721 uses all the SMBus communications protocol, except for packet error correction (PEC). The
charger IC address is (0x12), although it is not 100% SBS compliant. In most applications the extra functionality
provided by the differing SBS-Like interface enhances the control of the charger application, while simplifying the
interface block, using only the pertinent functions. Five 16-bit registers are used to interface between the
embedded host and the charge control IC. The Charging Voltage (0x15) register is used to set the battery
regulation voltage. The Charging Current (0x14) register is used to set the battery charge regulation current. The
Input Current (0x3F) register is used to set the input regulation current. The Charger Mode (0x12) control register
is used to set the charger operating modes. Finally, the Charger Status (0x13) register is used to monitor the
operating status of the charger.
ADDRESS
0x15
0x14
0x3F
REGISTER
Charging voltage
Charging current
Input current
DESCRIPTION
Used to set the battery regulation voltage.
Used to set the battery charge regulation current.
Used to set the input regulation current.
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