BQ76952: BQ76952 Host Watchdog Function.

Hello Song, 

The short answer to the questions is that it is possible to configure HWD to do the behavior you have mentioned above. 

Below is step-by-step examples of how this may be achieved:

• First, enable the REG1 regulator (set REG0 Config = 0x01, REG12 Config = 0x0D to set REG1 to 3.3V)
• In the Enabled Protections C register, set the [HWDF] bit to enable this protection.
• The time for this protection to trigger can be set in the Protections:HWD:Delay register. I set this to 5 seconds for this example.
• In the HWD Regulator Options register, set the [TOGGLE_OPT] bits to ‘10’ and the [TOGGLE_TIME] to ‘0101’ (see below image)

• Finally, disable the Dashboard in BQStudio (see image) to stop communication from the PC. This will cause the watchdog timer protection to trigger after 5 seconds and REG1 will turn off. Then after 5 more seconds (because of the TOGGLE_TIME bits), REG1 will turn back on.

Hopefully this answers your question!

Best,

-Luis T

Hi. Luis Torres

Thank you for your supprot.

According to your solution, there is a below problem.

*Assumption : MCU reset Active Low

*Problem Flow

1. when BQ76952 wake up from Shutdown Mode, voltage of REG1 chagne from Low(0V) to High (3.3V or 5V)

   : we should use shutdown mode....

2. At that moment, MCU reset because REG1 is Low and MCU reset Active Low

*Question

1. not REG1 and REG2, is there way to reset MCU such as ALERT pin?

   : ALERT pin is desinged with pull-up resistor. so, when BQ76952 wake up from shutdown, voltage of ALERT maintain High..

     therefore, when only occur host watchdog, can reset MCU (our thinking....)

Hi Song,

In the example Luis showed, the REG1 is configured to turn off when the MCU is not communicating and the turn REG1 on again. So REG1 will go from 3.3V to 0V, then back to 3.3V (the example can be modified based on the timing desired). Wouldn't this solve the problem of resetting the MCU?

Is the problem that when you put the BQ76952 into Shutdown mode, it will accidentally reset the MCU? Then maybe the Alert pin could be used. The Default Alarm Status register allows the Alert pin to signal if the device is going into Shutdown (SHUTV bit) or if a HWDF has occurred (SSBC bit). 

Can you help clarify these questions and we can try to think about the best solution.

Thanks,

Matt

Hi Matt Sunna

Thank you for support

According to your suggestion, there are some question.

Q1. According to your guide, we tested and could find ALERT Activation after host watchdog fault (below picture)

but, problem can't return to original status because it is impposible to clear host watchdog fault (due to communication fail status)

It cause repeated reset of MCU. is it way to return ALERT siganl in host watchdog falult status?  

Q2. Now, we use P/N BQ76952 (below green shadow) and REG1 LDO Default is disable

Can we change REG1 LDO Default to enable by OTP setting? (below yellow shadow)

Additionally, does BQ7695202 always have LDO1 output?

Q3. If above Q2 question is possible, our concern is the number of OPT writes.

As far as I know, the number of OTP writes is limited to 2.

If there is no additional write after OTP write in the factory, there will be no problem.

However, there is a concern that MCU reset occurs during use, and OTP write proceeds, exceeding the limited number of times.

Doesn't this matter?