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BQ78350: BMS Interfaces for Host uC for Battery Authentication

Kailash Patalay
Prodigy 135 points
Part Number: BQ78350

Hello,

We would like to have below functionality for battery pack BMS with bq78350:

1. Wake-up/Turn battery pack BMS/SMBus ON/OFF using a host-controlled latching ON/OFF switch (Can this be done using GPIO, KEYIN/PRES ?)

2. Perform SMBus SHA-1 authentication. If battery is authenticated by host uC, turn ON main battery pack output (CHG/DSCG FETs). Else turn OFF main battery pack output (FETs).

3. Host micro-controller for latching ON/OFF circuit and for SMBus communication to be powered by battery @ (3.3V/5V ~100s mA) ( using isolated DC-DC or GPIOs if possible). 

Please let us know the correct procedure & required BMS interfaces (GPIO, KEYIN/PRES, isolated DC-DC) to implement the above functionality.

If you are able to provide a reference schematic/circuit diagram with bq78350 to implement the above functionality, it would be much appreciated. 

Thank you very much.

Kailash

  • 0
    TI__Guru* 81034 points

    Hi Kailash,

    I think it is possible to implement much of this functionality, but this is going to be highly dependent on your host uC and its software. I can point you to documentation on each of these features for the BQ78350-R1, but you will need to determine how to configure your host uC setup and software.

    The KEYIN pin functionality is described in detail in Chapter 15 of the BQ78350-R1 Technical Reference Manual: http://www.ti.com/lit/pdf/sluubd3

    The PRES pin functionality is described in Chapter 6 of the same document. You can also look at the Enabled Removal Recovery and FET Options flash registers to see the options available.

    The device authentication features are described in Chapter 11 of the TRM. You host uC can decide whether to enable of disable FETs based on the result.

    There is also a Shutdown command which will completely power off the BQ78350-R1. To bring the device out of Shutdown, you need to toggle the Boot pin on the BQ769x0 companion AFE device. 

    You will need to figure out how you are going to interface the SMBus to a higher power controller since the BQ78350-R1 runs on a 2.5V regulator. This video provides some instructions on creating your schematic for the BQ769x0, and it also points you to multiple TI Reference designs that might be helpful. https://training.ti.com/how-create-schematic-bq76920-bq76930-and-bq76940 

    I hope this helps.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 135 points

    Dear Matt,

    Thank you for your helpful replies. 
    Regarding KEYIN & PRES pins, typically what sort of external hardware do the PINs interface to ? Is KEYIN intended to be used with some sort of toggle or latching on/off switch ? And is PRES pin looped to an external short to (VSS) GND PIN ? 
    Can you also clarify regarding the GPIOs pins and some use-cases for it ? Can GPIO pins also be used as a wake-up / sleep signal for the BMS with the external ON/OFF latching circuit ? 
    Regarding supply power to host uC, can the GPIO pin (or Vcc / other pin) of the bq IC be used to drive the host uC ? If so, what is the max. voltage & current levels that it can support ? If not, would we need to design an isolated DC-DC output from the battery pack output ? 
    Please suggest your recommended procedure for implementing the BMS wake-up & sleep function using an external latching on/off circuit; for initial low-power turn on for the SMBus SHA authentication; & then for full-pack power on/off after authentication.
    Also, if you can point us to a reference schematic for the bq769x0/78350 that shows the circuit design & use of the various interfaces above (KEYIN/PRES & GPIOs) to obtain this functionality that would be very helpful. 
    Thank you !
    Regards,
    Kailash
  • 0 in reply to Kailash Patalay
    TI__Guru* 81034 points

    Hi Kailash,

    The KEYIN input can be used to turn the DSG FET on and off, for example in an e-bike that you want to turn on/off with a keyswitch.

    The PRES pin is to detect whether a removable pack is inserted and turn the FETs on or off depending on the state.

    The GPIOs do not have any real functionality - they can be set as outputs of a specific state through SMBus commands or they can be set as inputs and the state can be read through SMBus commands. They are not used to control functionality of the device.

    Power for the host MCU can maybe be supplied from the REGOUT pin of the BQ769x0 device. This also powers the BQ78350-R1, so make sure this matches the voltage you need and that you are still within the current range. It is 2.5V for the BQ78350-R1.

    For the remaining questions below, we do not have the specific examples you are requesting. Each system is unique and different users have vastly different solutions based on how they need to control their power modes and FETs.

    Please suggest your recommended procedure for implementing the BMS wake-up & sleep function using an external latching on/off circuit; for initial low-power turn on for the SMBus SHA authentication; & then for full-pack power on/off after authentication.
    Also, if you can point us to a reference schematic for the bq769x0/78350 that shows the circuit design & use of the various interfaces above (KEYIN/PRES & GPIOs) to obtain this functionality that would be very helpful. 
    Best regards,
    Matt