The BQ77307 device includes Data Memory registers with values stored in digital logic, as well as one-time programmable (OTP) memory, which holds device trim
information and default settings for registers. At initial power-up or after a reset, the device loads the OTP settings into registers, which are used by the device logic during operation. If the device is unsealed, it can also perform a
reset on demand if the 0x0012 RESET() subcommand is sent. Register values are preserved while the device is in NORMAL mode. If the device enters SHUTDOWN mode or a reset occurs, all register memory is cleared, and the device returns
to the programmed OTP parameters when powered again.
The OTP memory is written by TI during device manufacturing and cannot be modified by the customer. A customized OTP configuration can be developed and programmed into a custom device by TI,
depending on business terms.
The device supports several different potential use cases:
- Standalone operation - a customized OTP configuration is programmed into a custom device by TI. At each powerup of the device, it loads settings from OTP and operate autonomously
without needing any host processor interaction. The I2C bus on the device is not connected. If interested in this option, please contact TI for further discussion.
- Autonomous operation with status information - as above, the device is configured using a customized OTP programmed by TI. While the device does not require host
interaction, a host processor can receive an interrupt whenever a protection alert or fault occurs and can query the device over I2C to determine what event initiated the interrupt. In this case, the host processor is not
involved in configuring protection settings, so is not necessarily involved in safety critical functionality. The OTP configuration can optionally allow the host processor to control the FET drivers over I2C, or they can
be set for only autonomous operation by the device itself.
- Autonomous operation with configuration/status access - as in Autonomous operation with status information, the device OTP is programmed by TI into a custom device, and
the host processor can receive interrupts and check status information over I2C. In addition, the host can use a security key to unseal the device and modify settings in registers from their preprogrammed values loaded
from OTP.
- Programmable operation with configuration/status access - if a custom device from TI with OTP preprogrammed with settings is not desired or practical, then the device can be
configured by a host processor over I2C, either in the field or on the customer production line. In the field, any time the device is powered from SHUTDOWN mode, the host can configure the desired settings before the FETs
are enabled. If a host processor is not included in the pack, then the customer can program the device on the production line, then leave it powered continuously thereafter in field operation. Status information is also available
over I2C during operation, even if the settings have been locked with the security key.
The OTP memory also includes a digital signature, which is stored in OTP. When the device is first powered or after a reset, it reads the OTP settings and check that the signature matches that
stored, to provide robustness against bit errors in reading or corruption of the memory. If a signature error is detected, the device enters SHUTDOWN mode.