BQ27425-G1 Datasheet, PDF (17/32 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated Sense Resistor

bq27425-G1
www.ti.com
SLUSAI6 – NOVEMBER 2011
Occasionally, a data CLASS will be larger than the 32-byte block size. In this case, the DataBlock( ) command is
used to designate which 32-byte block the desired locations reside in. The correct command address is then
given by 0x40 + offset modulo 32. For example, to access Terminate Voltage in the Gas Gauging class,
DataClass( ) is issued 80 (0x50) to set the class. Because the offset is 48, it must reside in the second 32-byte
block. Hence, DataBlock( ) is issued 0x01 to set the block offset, and the offset used to index into the
BlockData( ) memory area is 0x40 + 48 modulo 32 = 0x40 + 16 = 0x40 + 0x10 = 0x50.
Reading and writing subclass data are block operations up to 32 bytes in length. If during a write the data length
exceeds the maximum block size, then the data is ignored.
None of the data written to memory are bounded by the bq27425, the values are not rejected by the fuel gauge.
Writing an incorrect value may result in hardware failure due to firmware program interpretation of the invalid
data. The data written to NVM blocks is persistent, so a power-on reset does not resolve the fault.
ACCESS MODES
The bq27425 provides three security modes (FULL ACCESS, UNSEALED, and SEALED) that control data NVM
access permissions according to Table 6. Although FULL ACCESS and UNSEALED modes appear identical,
only FULL ACCESS mode allows the bq27425 to write access-mode transition keys.
Table 6. Data NVM Access
Security Mode
FULL ACCESS
UNSEALED
SEALED
Data NVM
R/W
R/W
None
Manufacturer Info
R/W
R/W
R
SEALING/UNSEALING DATA BLOCKS
The bq27425 implements a key-access scheme to transition between SEALED, UNSEALED, and
FULL-ACCESS modes. Each transition requires that a unique set of two keys be sent to the bq27425 via the
Control( ) control command. The keys must be sent consecutively, with no other data being written to the
Control( ) register in between. Note that to avoid conflict, the keys must be different from the codes presented in
the CNTL DATA column of Table 2 subcommands.
When in SEALED mode the [SS] bit of CONTROL_STATUS is set, but when the UNSEAL keys are correctly
received by the bq27425, the [SS] bit is cleared. When the full-access keys are correctly received then the
CONTROL_STATUS [FAS] bit is cleared.
Both the sets of keys for each level are 2 bytes each in length and are stored in data ROM. The UNSEAL key
(stored at Unseal Key 0 and Unseal Key 1) and the FULL-ACCESS key (stored at Full Access Key 0 and Full
Access Key 1) can only be updated when in FULL-ACCESS mode. The order of the bytes entered through the
Control( ) command is the reverse of what is read from the part. For example, if the 1st and 2nd word of the
UnSeal Key 0 returns 0x1234 and 0x5678, then Control( ) should supply 0x3412 and 0x7856 to unseal the part.
Copyright © 2011, Texas Instruments Incorporated
17