SLUUBD4A April 2016 – November 2022 BQ27220
The fuel gauge implements a key-access scheme to transition from SEALED to UNSEALED mode. Once SEALED via the associated subcommand, a unique set of two keys must be sent to the fuel gauge via the Control() command to return to UNSEALED mode. The keys must be sent consecutively, with no other data being written to the Control() register in between. When in SEALED mode, the OperationStatus[SEC] bits (SEC1,SEC0) are set to 11; but when the Sealed to Unsealed keys are correctly received by the fuel gauge, the [SEC] bits (SEC1,SEC0) transition to 10. The Sealed to Unsealed key has two identical words stored in ROM with a value of 0x8000 8000; therefore, Control() should supply 0x8000 and 0x8000 (again) to unseal the part.