TPS65381-Q1: Purpose of device inside EEPROM

Hi Sinichi,

The EEPROM is used internally to the device to trim various funcitons. There is no direct access to it, however when BIST is run at power up the CRC value for the EEPROM is checked as part of BIST. This may also be manually run by the MCU via the CRC registers.

The SPI controlled registers are not non-volital memory, depending on the event a power on reset event with reset all registers to their initialized state, and for any event that causes RESET assuming AUTO_BIST_DIS = 0 (default), when the TPS device transitions from RESET state to DIAGNOSTIC state BIST will be run and the list of registers in the LBIST section will be re-initialized after LBIST has completed.

Scott

Hi Shinichi-san,

Let me explain a different way.  There is one CRC8 calculation engine within the TPS65381, however it is used to compare two different CRC options.  The first is automatically run at power up as part of the ABIST sequence, that is to compare the internal (non customer accessible EEPROM registers vs an internal EEPROM CRC value for those EEPROM values).  EEPROM is used to "trim" the device for accuracy at TI production test.  Once TI tests the device it is never updated and not accessible to the customer. If EEPROM would fail it could lead to out of specified operation so the CRC for EEPROM provides diagnostic coverage against such an occurrence.  The same CRC8 calculation engine can be used by customers.  Once they have configured (written) the device registers for the settings needed for their specific application, they (the MCU software) calculates the CRC8 value and loads that to the SAFETY_CFG_CRC register.  When the CFG_CRC_EN bit is set, the TPS65381 will read all the covered registers and calculate internal to the deivce the CRC8 value and compare it to the value in SAFETY_CFG_CRC.  This diagnostic helps provide coverage against SPI input errors, register bit flips, etc for the customer configuration registers. 

The customer (MCU/Software) can run either the register CRC or EEPROM CRC at any time via the process outlined in the "Device Configuration Register Protection" section of the datasheet.

Answers to questions:

A1:  EEPROM is not effected by SPI under any case

A2: EEPROM CRC that is internally stored in the device is not impacted by SPI or customer register configurations.   The CRC stored in SAFETY_CFG_CRC is for the listed configuration registers.  The customer must calculate the correct CRC8 value for this register to match how they configure the listed registers covered by the register CRC (64-bit string listed in the datasheet).

A3:  EEPROM is never updated, but has to be checked against potential data retention issue that could impact device operation (diagnostic coverage).

A4: As outlined above EEPROM is TI internal to "trim" electrical performance plus the CRC value for these EEPROM trim bits.  All EEPROM bits are internal and not customer accessible.

A5: The TPS calculated the CRC for registers is compared to the stored in SAFETY_CFG_CRC when the CFG_CRC_EN bit is set and the procedure from Device Configuration Register Protection" section of the datasheet is used, if the procedure listed there is continued to step 5-10 the EEPROM CRC is re-calculated and compared to the internally stored CRC for EEPROM as the next part of the procedure.

Hopefully that helps clarify this topic.  We also have a datasheet revision underway that should post to the ti.com site within a few weeks where this procedure has been updated a little to make it more clear.

Scott