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TPS65381-Q1: using only analog section and not the digital state machine

Needhu Gunasegaran
Intellectual 2890 points
Part Number: TPS65381-Q1
Other Parts Discussed in Thread: TPS65381A-Q1

Hello,

My customer has the following questions,

Our hardware engineers are wondering if it is possible to use only the analog part (power supply for the periphery eg: TMS570) and to not use the digital part (specially for the SPI interface between the TPS65381A-Q1 and TMS570, so as to not use the internal complex state machine)?

 since according to the manual of the Safety Companion TPS65381A-Q1 (SLVSDJ1A) says that in the event of an over temperature condition, the VDD5 regulator should be activated and re-enabled via the SPI interface. The same is true with the VSOUT1 regulator, which is disabled by default and needs to be activated via the SPI interface.

Another aspect that bothers me a bit is the internal digital state machine of the companion chip. There are various transitions to various states that require an SPI connection in order to react to the watchdog timeout (DIAGNOSTIC -> ACTIVE or DIAGNOSTIC -> SAFE).

 Can the TPS65381A-Q1 be used independently only for the analog part or power supply for the periphery? Or does an interaction with the digital part have to be considered?

Looking forward for a reply.

Thanks,
Needhu

  • 0
    TI__Mastermind 20590 points

    Hi Needhu,

     

    The TPS65381A-Q1 was developed as a companion power supply with diagnostic and protection features to be used with the TMS570/Hercules in functional safety applications so it is not a typical request that a customer doesn’t want to use them.  

     

    If your customer really wants to use this device as just a PMIC and not use the extra features and diagnostics, there is a simple scenario where the device can be used as a power supply without needing to use the SPI. 

     

    If the PMIC is powered up and never configured via SPI, it will timeout internally to it’s SAFE state. In this case, the device will power up and time out into its internal SAFE state with the following rails power up and remaining powered:   VDD6 pre-regulator, VDD5 (5V), VDD3/5 (normally IO or single supply for MCU, configurable for 3.3V or 5V) and VDD1 (adjustable LDO controller with external FET, normally core supply to MCUs needing higher current or 1.x V core supplies so 1.23 V for TMS570).  There is no way to enable VSOUT1 (normally used as a sensor supply) without using SPI.

     

    In case any of the diagnostics that are integrated into the PMIC to support functional safety detect an issue the protection action will take place.

     

    By not using the digital features such as Q&A watchdog and MCU error signal monitor, I assume the system is adding equivalent diagnostic coverage somewhere else in the system to for these critical MCU monitoring functions.

     

    The SafeTI Diagnostics library for the TMS570/Hercules includes the drivers and code for the TPS65381x-Q1 so it should be straight forward to use the SPI and other functions.

     

    It may be that this customer and application safety goals and assumptions are very far away from those of the TPS65381A-Q1.  This is quite unusual since the TPS65381A-Q1 is used in many applications where the features added to the PMIC to support functional safety are used to support the systems’ overall functional safety goals and design.

     

    Best Regards,

    Scott