BQ26150 Datasheet, PDF (5/16 Pages) Texas Instruments – BATTERY PACK SECURITY AND AUTHENTICATION IC FOR PORTABLE APPLICATIONS (bqSECURE)

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Pack +
HDQ
bq26150
SLUS641A – JANUARY 2005 – REVISED JULY 2005
APPLICATION INFORMATION
Optional Battery Monitor/Gas Gauge
R3
5 kW
0.01 mF
5
4
bq26150
1 23
Protector
R2
100 kW
V_CC
V_SS
HDQ
GPIO
SRP
SRN
BAT
+
R1
0.02 W
Pack -
Figure 2. Typical Application Circuit
FUNCTIONAL DESCRIPTION
The bq26150 provides a simple and cost effective method to authenticate battery packs for end equipment.
Security is achieved through the use of a 16-bit CRC, a 16-bit CRC seed, a 96-bit device ID, and a 32-bit random
challenge. The CRC polynomial, CRC seed, and 96-bit ID are unique from device to device, and are stored as
encrypted text in public memory, and as plain text in private memory. The host system can decrypt the
polynomial, seed, and ID values using a shared key that is stored in end-equipments memory. The encryption
method and shared key used to store the polynomial coefficients and the device ID can be selected by the
manufacturer. Contact TI for information regarding specifics for encryption of the device ID and CRC polynomial
coefficients.
To authenticate a battery pack, the host reads the encrypted device ID, polynomial, and seed values. It decrypts
those values, then generates a 32-bit random challenge, which is transmitted to the bq26150. The bq26150 uses
the plain-text version of the polynomial coefficients and device ID, along with the 32-bit random challenge from
the host, to calculate the authentication CRC value. The host uses the polynomial coefficients, seed, and device
ID that it decrypted, along with the 32-bit random challenge it sent to the bq26150, to calculate the authentication
CRC value. When the host and bq26150 have completed the calculations, the host can read the authentication
CRC value the bq26150 computed and compare to its own value. If the values match, the battery pack is
authenticated.
The bq26150 has a communication pass-through mode that allows it to be used in systems with an existing HDQ
based battery monitor or gas gauge. Once the battery pack is authenticated, the bq26150 can be put in
continuous pass-through mode, allowing the host system to communicate with a second HDQ device with no
additional overhead. A one-time pass-through mode is also available, allowing the host to communicate once to
the second HDQ device as needed.
The bq26150 obtains the power needed to run from the HDQ bus. An external capacitor is charged when the bus
is high and discharges while the bus is low. If the bq26150 is not authenticating or communicating and the HDQ
bus is low, the power is reduced and it enters sleep mode. If the bus is held low until the capacitor fully
discharges, the bq26150 is disabled.
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