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BQ78350 - BQ769x0 shutdown/ship mode

Michal Solecki
Intellectual 295 points
Other Parts Discussed in Thread: BQ76920, BQ78350

Hi,

We are currently developing with the BQ78350 with the BQ76920 AFE interface. The firmware version on the BQ78350 is: 1E9B_0_06.

We are trying to enter shutdown mode, however, we can't seem to get the behaviour that we would expect.

Our understanding was that the shutdown mode command to the BMS (MAC command 0x0010) would also be forwarded to the AFE. Therefore, the AFE would fall into SHIP mode.

If that's the case, we would expect the internal and external LDOs of the AFE to be turned OFF, however, we can still read a voltage at the REGOUT and CAP1 pins.

To enter SHUTDOWN mode, we made sure that the DSG bit was set using BQ studio. We then sent  the command twice by using the SHUTDOWN button on the BQ studio GUI. We also assumed that BQ studio would stop getting readings from the BQ78350 since it would be shut down.

We were surprised to see that the BQ studio still gave us readings. We also saw that the SDM bit (Operation status) was changed to 1. We also saw that the XDSG and DSG bits were also set to de-activate the FETs.

Ideally, in our case, we wanted the LDOs to be stopped so the BQ78350 would be stopped. But we are either not following the correct procedure to send the BQ78350 into shutdown, or our understanding is not correct.

Here are some questions that help us clarify what is going on:

1- What is the behaviour of the BQ78350 in shutdown mode? (i.e.which modules are ON and which ones are OFF)

2- Is the shutdown command forwarded to the AFE to enter SHIP mode?

3- How do we verify that the AFE is in SHIP mode?

4- In SHIP mode, do the LDOs still work? Can they be stopped (at least the external one)

5- If that is not the expected behaviour, is there a way to send the AFE into ship mode?

Thank you in advance for your help.

  • 0
    TI__Guru 54715 points

    1. Typically after the shutdown command is received there is a several second delay and the AFE will power down.  The gauge continues its operation until the shutdown occurs.

    2. The shutdown command will normally cause the gauge to send the ship sequence to the AFE.

    3. The AFE is in ship mode if the REGOUT and CAP1 pins go to ~ 0V.

    4. In Ship mode the REGOUT and CAPx regulators are off.

    5. Only 1 shutdown command should be needed, otherwise your sequence seems correct.  Check to see if there is a charge current shown on the gauge from an applied current, an odd threshold setting, or a mis-calibration.  Applying a charge current is a typical method to prevent low voltage shutdown to keep the system awake to allow correction of mis-configuraiton, it may prevent MAC command shutdown as well.

  • 0 in reply to WM5295
    Intellectual 295 points
    It now works!
    You were correct, there was a mis-calibration in the CC offset. When the FETs were shut off, the BQ78350 would see a small but not negligable charge current and therefore would not shut down.
    Thank you very much.