BQ76942: OTP write on permanent failure

Hi Erik,

Are you reading the SAVED_PF_STATUS() after you start the AFE and it is no longer showing the PF occurred?

The voltage levels for writing the PF do not need to be special. It should work under normal conditions.

Regards,

Matt

Hi Matt!

Yes, exactly. If an OTP write of the PF would have been performed, we believe that the SAVED_PF_STATUS() would reflect this - even after a shutdown. Instead, it's reset to zero. We wonder if you could think of any missed criteria for writing the OTP?

Best regards

//Erik Almqvist

Hi Erik,

As far as I can tell, your settings are correct (PF_OTP and OTPW_EN are both set). I will test this on a device tomorrow to verify. I don't want to do the experiment on an EVM since it has a permanent effect.

Best regards,

Matt

Thanks for your support Matt, please update on your findings!

We assume the OTP write would occur quite fast (e.g seconds...) after the PF flag has been set, is that correct?

The reason I asked is vague. In one test we did see a reset (that we can't pinpoint the reason for), about a minute after the PF occurred. We figured the OTP should have been written at this point, but it might be worth confirming. Manual states that a reset (e.g. via shutdown pin) do reset the PF. (We've also lost the PF in other tests.)

Hi Erik,

I tried this with the same steps, except I caused an SUV PF (I don't have access to a high voltage lab at the moment). After entering and exiting Shutdown, I still see the SUV is triggered and the SAVE_PF_STATUS() shows the condition was saved.

The OTP programming should be slower since the voltage is beyond the 10-12V range, but I would expect 30 seconds to be plenty of time. 

Matt

Hi!

Thanks for your investigations Matt! We did found out what's wrong in our case. Sorry for breaking your hardware from the other side of the globe.

The reason we had what we did is that we did manage to trigger a reset signal from MCU when re-configuring the AFE after a shutdown. And, as stated in the manual, a reset via PIN do reset the SAVED_PF_STATUS register. We came to this conclusion after some debugging using BQStudio and an erased MCU. We must check this register directly after startup.

We have some follow-up question in order for us to take the best route going forward.

A.) The manual uses the terminology "full reset" in some cases without elaborating on when a full reset occurs. Is it only a shutdown that leads to a full reset?
B.) Is there any functional differences between a RESET 0x0012 command and a RST_SHUT (pin reset)?
C.) What is the best way of knowing that a OTP write of PF has completed? Is 10 seconds enough?
D.) What is the transition of "Very Low VBat" from Deepsleep mode to Shutdown mode in Figure 7.1 ("Operational modes") of the BQ76942 manual.

The reason for asking A.) and B.) is that we had a reset implemented as part of our configuration sequence. This was done in order to handle removal of a configuration parameters by issuing a reset (thus reset to default). As this doesn't seem to work and we'll check if we should change to only performing a reset in other special error. But we find the usage of reset / full reset a bit unclear in the manual.

Best regards
//Erik Almqvist

Found the answer to D.) myself

"if the BAT pin voltage falls below VPORA - VPORA_HYS, the device transitions to SHUTDOWN mode"

BR

//Erik Almqvist

Hi Erik,

Sorry for the delay - I was out of office the past couple days. 

The RESET 0x0012 command does a full reset of all of the device registers. The reset using the RST_SHUT pin is only a partial reset - it does not clear the device register settings and it will not clear the PF.

A Shutdown and re-boot will be similar to the RESET 0x0012 command in that it will completely reset all registers back to defaults (or to OTP programmed values if OTP has been programmed).

I think 10 seconds should be plenty of time for the OTP to write. It should complete faster than this, but  I do not know the exact timing.

Best regards,

Matt

Thanks Matt!

No worries about the delay, I think this forum works excellent for this type of support, and that you respond very fast!

Do you know if a full reset have any impact on the REGx output that we use to power the MCU, or is this respected by AFE if OTP programmed to stay on? If If this is the case, I assume we should use the POR bit after setup to check if a configuration is needed...

Best regards

//Erik Almqvist

Hi Erik,

If it is programmed in the OTP, then the OTP settings will be the defaults, so a full reset should not affect the REGx ouptut.

Best regards,

Matt