BQ26150 Datasheet, PDF(8/16 Page) Texas Instruments – BATTERY PACK SECURITY AND AUTHENTICATION IC FOR PORTABLE APPLICATIONS (bqSECURE)

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BQ26150 Datasheet, PDF (8/16 Pages) Texas Instruments – BATTERY PACK SECURITY AND AUTHENTICATION IC FOR PORTABLE APPLICATIONS (bqSECURE)

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bq26150

SLUS641A â JANUARY 2005 â REVISED JULY 2005

www.ti.com

DONE

DONE is set when bq26150 has completed calculating the CRC after AUTH bit has been set. This

is a flag to the host system that the message/authentication registers contain the calculated CRC

value. The bit is automatically cleared when the AUTH bit is set.

AUTH

Writing this bit to 1 initiates the CRC calculation. The message written to the message/digest

registers, 0x03 â 0x00, are used as input. This bit is automatically cleared when the CRC

calculation is complete and the authentication value has been written to the message/authentication

registers.

Authentication CRC Value (AC) â Addresses 0x05 â 0x04

The value computed from the CRC. The register is cleared on POR. This register cannot be written by the host

system

Random Challenge (RC) â Addresses 0x03 â 0x00

The host system writes this register set with a random challenge that is used to calculate the CRC value (see

below for details on the CRC calculation). The bq26150 uses the entire 4 bytes to calculate the CRC when the

AUTH bit (CTRL[0]) is written to 1. After the authentication value is calculated, bq26150 writes the digest to the

AC registers, clear the AUTH bit and set the DONE bit (CTRL[1]).

CRC Description

A CRC, or cyclic redundancy check, is normally used to detect small errors in the transmission of data. A CRC

calculation is a form of polynomial modulo 2 arithmetic, so a CRC is usually referenced by means of a

polynomial, i.e., 1 + x4 + x5 + x16. Most correct CRC polynomials ensure that the highest and lowest polynomial

orders have a coefficient of 1. The highest order coefficient represents the number of bits in the final CRC value

and the other terms with a coefficient of 1 represent the tap points where an XOR is performed. The example

CRC 1 + x4 + x5 + x16 would then represent a 16 bit CRC value, with tap points at the x5, x4, and x0 stages. The

bq26150 uses a 16 bit type 2 linear feedback shift register with programmable tap points. This allows the CRC

polynomial to vary from device to device.

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