Rainbow Electronics DS2784 - Manual (Page 6)

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
DETAILED DESCRIPTION
The DS2784 functions as an accurate fuel gauge, Li+ protector, and SHA-1-based authentication token. The fuel
gauge provides accurate estimates of remaining capacity and reports timely voltage, temperature, and current-
measurement data. Capacity estimates are calculated from a piecewise-linear model of the battery performance
over load and temperature, and system parameters for full and empty conditions. The algorithm parameters are
user programmable and can be modified in pack. Critical capacity and aging data are periodically saved to
EEPROM in case of loss of power due to a short circuit or deep depletion.
The Li+ protection function ensures safe, high-performance operation. nFET protection switches are driven with a
9V charge pump that increase gate drive as the cell voltage decreases. The high-side topology preserves the
ground path for serial communication while eliminating the parasitic charge path formed when the fuel gauge IC is
located inside the protection FETs in a low-side configuration. The thresholds for overvoltage, overcurrent, and
short-circuit current are user programmable for easy customization to each cell and application.
The 32-bit wide SHA-1 engine with 64-bit secret and 64-bit challenge words resists brute force and other attacks
with financial-level HMAC security. The challenge of managing secrets in the supply chain is addressed with the
compute next secret feature. The unique serial number or ROM ID can be used to assign a unique secret to each
battery.
BLOCK DIAGRAM
6 of 38