Atmel has introduced its high-voltage technology AVR microcontroller that implements full 2-4 cell Lithium Ion smart battery monitoring and protection on a single chip.
Lithium Ion (Li-ion) is the battery chemistry of choice for high-end portable applications such as laptop PCs, cellphones and digital cameras, due to its high energy per weight and volume ratio, combined with a high load current. A Li-ion-based battery control system must control the chemical reaction and protect the system from harmful environmental conditions. Furthermore, the end-user expects the battery control system to deliver a reliable and accurate estimate of charge left. Atmel claims its ATmega406 single-chip smart battery device is the only product with everything needed to meet these challenges with highest accuracy and reliability at the lowest system cost.
The device includes an on-chip voltage regulator allowing the device to be powered from 4-25 V. It also features three 25 V-tolerant FET drivers for charge, discharge, and pre-charge, as well as on-chip FETs for cell balancing. To provide the most accurate estimate of charge left, the device has a Coulomb Counter ADC with an 18-bit output for battery current monitoring as well as a 12-bit ADC for individual cell voltage and temperature monitoring. Both ADCs use high-accuracy on-chip voltage reference. Battery protection is autonomous, providing the end-user with the best safety, as MCU-related issues such as a code runaway or a software bug do not affect it.
Battery protection is implemented as independent circuitry, not requiring the MCU to operate. If the device is exposed to an over-current or short-circuit condition, the autonomous battery protection will shut off the affected FET. Likewise, if any cell voltage drops to a potentially damaging voltage level, ATmega406 will automatically prevent further battery discharge by shutting down the discharge FET and going to a power-off mode.
The current resolution of the Coulomb Counter over the recommended 5 mΩ sense resistor is 0,67 mA, allowing measurements of more than ±30 A. Both ADCs benefit from a very accurate internal voltage reference, with less than ±0,1% error over temperature after calibration.
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