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Stand-Alone Fuel Gauges Integrates a Li+ Protector and SHA-1 Authentication

5th May 2009

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Datasheet

Maxim has introduced the DS2775/DS2776/DS2777/DS2778, said to be the industry's first 2-cell, stand-alone fuel gauges to integrate a 2-cell lithium-ion (Li+) protector in a tiny, 3mm x 5mm TDFN package. Additionally, the DS2776/DS2778 integrate SHA-1 authentication for battery security. These devices consume 75% less board space than the leading competitive solution, which requires three discrete ICs to implement the same security functionality as the DS2776/DS2778.

The DS2775-DS2778 enable the implementation of small, low-profile Li+ battery packs, making them ideal for low-cost notebooks, UMPCs, DSLR cameras, video cameras, commercial and military radios, portable medical equipment, and other space-constrained, portable applications that use 2-cell Li+ battery packs.

The DS2775-DS2778 fuel gauges estimate available capacity based on coulomb count, discharge rate, temperature, and cell characteristics. To reduce development effort and time-to-market, these devices combine a precision, analog front-end for measuring current and voltage with a proprietary, embedded FuelPack(TM) fuel-gauge algorithm. On-chip temperature measurements eliminate the need for a thermistor in the battery pack. Additionally, these fuel gauges can use temperature data to enable gain and temperature-coefficient compensation in the current measurement, thereby allowing the use of a low-cost current-sense resistor.

The integrated 2-cell Li+ protector monitors for cell overvoltage, undervoltage, overcurrent, and short-circuit conditions. Thresholds are user-programmable and can be locked to prevent accidental overwrites. A built-in charge pump enables cell protection to be implemented with low-cost, low-RDS(ON), high-side n-channel FETs. The Li+ protector also allows the host system to communicate with the battery pack, even during a fault condition.

The DS2776/DS2778 integrate a secure challenge-and-response authentication algorithm that provides exceptional protection against the counterfeiting of battery packs, thereby increasing safety and reliability for the end user and protecting the reputation of the product manufacturer. These fuel gauges utilize a SHA-1 algorithm with a 64-bit secret and communicate with the host over a 1-Wire(R) interface.

In addition to nonvolatile storage for cell compensation, application parameters, cycle counter, and age estimation, the DS2775-DS2778 integrate 16 bytes of EEPROM memory to facilitate battery lot and date tracking or nonvolatile storage of system and battery-usage statistics.