DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication

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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

FuelPack™

Algorithm

POWER MODE

Control

PRECISION

ANALOG

OSCILLATOR

16 Byte User

EEPROM

1-Wire Interface

CHARGE

PUMP

VDD

VDD_INT

CP

CURRENT

(VSS - SNS)

TEMPERATURE

VOLTAGE

(VIN - VSSA)

VIN

VREF

DS2784

10-Bit + sign

ADC/MUX

SNS

VSS

PIO

DQ

WKP, WKD

LITHIUM ION

PROTECTOR

PLS

FET DRIVERS

CC

DC

UV, CD

32 Byte

Parameter

EEPROM

Pin Drivers

and Pwr

Switch

Control

PIO Logic

15-Bit + sign

ADC

Control and

Status Registers

FuelPack™

ALGORITHM