1- to 4-Cell Multi-Chemistry Synchronous Buck Battery ChargerMarch 16, 2020 by Paul Shepard
The BQ24800 from Texas Instruments is a high-efficiency, synchronous buck battery charger, offering low component count for space-constrained, multi-chemistry battery charging applications. The BQ24800 device supports hybrid power boost mode. Hybrid power boost mode boosts the battery up to the system voltage in order to supplement the adapter when system power demand is temporarily higher than the adapter is able to provide. The ultra-fast transition from battery charging to battery discharging prevents adapter crash from overloading condition.
The BQ24800 device also supports battery only boost mode when no adapter is present. When the battery voltage is above the minimum system operation voltage, the battery is directly connected to the system supply rail through BATFET. Once the battery voltage goes below the minimum system operation voltage, BQ24800 will turn on the boost mode to regulate the system supply rail, extending the system run time.
The BQ24800 device uses two charge pumps to separately drive N-channel MOSFETs (ACFET, RBFET, and BATFET) for automatic system power source selection.
Through SMBus, a system power management microcontroller programs input current, charge current, discharge current, and charge voltage DACs with high regulation accuracy.
The BQ24800 device monitors adapter current (IADP), battery discharge current (IDCHG), and system power (PMON) for host to throttle back CPU speed or reduce system power when needed. The BQ24800 device charges 1-, 2-, 3-, or 4-series Li+ cells.
Summary of Features
- Hybrid Power Boost Mode to power up system from adapter and battery together
- Ultra-fast transient response of 150 µs to enter Hybrid Power Boost Mode
- Battery Only Boost Mode to extend battery run time
- Peak power two-level input current limit to maximize the power from adapter and minimize battery discharge
- Charge 1- to 4-cell battery pack from 4.5- to 24-V adapter
- High accuracy power and current monitoring for CPU throttling
- Comprehensive PROCHOT profile
- ±2% Current monitor accuracy
- ±5% System Power Monitor Accuracy (PMON)
- Automatic NMOS power source selection from adapter or battery
- ACFET Fast turn on in 100 µs when exiting learn mode from battery removal
- Programmable input current, charge voltage, charge and discharge current limit
- ±0.4% Charge voltage (16-mV/step)
- ±2% Input current (64-mA/step)
- ±2% Charge current (64-mA/step)
- ±2% Discharge current (512-mA/step)
- High integration
- Battery LEARN function
- Battery present monitor
- Boost Mode indicator
- Loop compensation
- BTST Diode
- Enhanced safety features for over-voltage protection, over-current protection, battery, inductor, and MOSFET short-circuit protection
- Switching frequency: 300kHz, 400kHz, 600kHz, and 800kHz
- Realtime system control on ILIM pin to limit charge and discharge current
- 65-mA adapter standby quiescent current for Energy Star