Intelligent battery charger/power management IC enables simultaneous charging and system operation

Date: 14 Mar 2007

Synopsis: Portable system designers who want to guarantee that the battery charges at maximum available current during simultaneous system operation must typically build that functionality into the system with discrete components. By continuously monitoring the power needs of the system during operation and automatically adjusting charge current accordingly, AnalogicTech�s AAT3670 delivers the highest possible charge current to the battery and thereby minimises battery charge time, while reducing parts count, BOM and PCB board space requirements.

The AAT3670 is a highly integrated 1.6A dynamic battery charger and power manager IC for portable systems powered by single-cell Lithium-ion/polymer batteries. Integrating a battery charger, current-limited load switches and control circuitry, this highly intelligent device allows users to simultaneously charge their battery and run their system from an AC adapter or USB port without compromising the battery’s charge cycle life and without adding external load switches. The AAT3670 delivers the highest possible charge current to the battery and thus enables the consumer to experience the fastest possible battery charge time.

The AAT3670 provides dynamic power sourcing to the system load by managing the distribution of power between the source, the battery and the system simultaneously. If the system load exceeds the input supply current capability from the AC adapter or the USB port, the AAT3670 can source additional current from the battery.

A voltage-sensing charge reduction loop monitors the AC adapter input and USB input voltages and automatically prevents voltage sags by throttling back the charge current on the battery depending upon how much current the system load requires. By automatically adjusting charge current only to the extent necessary to maintain input source voltage integrity, this feature helps to simultaneously ensure continuous system operation and minimise battery charge time.

Under heavy load conditions, depending on PCB layout, the internal IC temperature may increase. Traditional thermal protection is a simple thermal shutdown. Since the AAT3670 supplies power to operate the system, such a shutdown is considered a fault condition and cannot be tolerated. Therefore the AAT3670 contains a digital thermal loop that measures the internal die temperature and reduces charge current if the die temperature exceeds the threshold. Since the battery charger does not get shut down, the digital thermal loop maximises charge current, given the set of operating conditions.

Battery charge levels on the AAT3670 can be programmed up to 1.6A for AC adapter charger, 0.9A for USB high and 0.1A for USB low charging. Low battery-to-system on resistance minimises power dissipation and voltage headroom.

The AAT3670 monitors battery temperature and charge states for a variety of fault conditions including over-voltage, short-circuit and over-temperature. In the event of a fault, the charger will automatically shut down to protect the charging device, the control system and the battery. A battery charger timer also protects the battery and system by terminating charging if the user-programmed charge time is exceeded. Two status monitor output pins are provided to indicate battery charge status via external LEDs.

AnalogicTech’s AAT3670 is available now in a Pb-free, thermally-enhanced, 24-pin 4x4-mm QFN package.