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BQ40Z80: Emergency Shutdown Operation via SHUTDN Pin

Antonio Fadhel
Genius 9410 points
Part Number: BQ40Z80

Hi,

The bq40z80 datasheet and TRM have very few detail regarding using SHUTDN\ as emergency shutdown input. This was my interpretation based on information from the description and other uses of the pin (such as PRES\):

• The pin is already biased internally through the resistor to the PBI pin.
• A typical use-case would be a pushbutton to GND at the pin to generate the high-to-low transition.
• Based on the PRES description, and assuming it applies to SHUTDN as well, the pin is sampled for 4us (enabling RHOEN) at a frequency of 1Hz. Current flow while sampling will be PBI_voltage/10k (8k min, 10k typ resistor).

However, when my customer tried to verify this behavior it was different from the above (appears as a 5V source with a 140k source resistance and a switched pulldown resistor). Can you please share some detail on the expected SHUTDN\ behavior when configured for emergency shutdown?

I can share more details of the findings offline if needed.

Thanks,

Antonio

  • 0
    TI__Guru** 105760 points

    Hello Antonio,

    We have assigned this to someone knowledgeable with the BQ40Z80 and he will get back to you shortly.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Mastermind 42060 points

    Hello Antonio,

    Would you mind sharing the .gg files of the set-up?

    I measured the pin on my EVM during the Emergency Shutdown configuration. The pin seems to cycle through different voltage levels from ~2mV to ~17mV every second. When the pin goes low during this period, it will toggle the EMSHUT register, disabling/enabling the FETs.

    I also think that the internal resistance is probably very large, definitely larger than 10-kOhm. So it might be possible that it is going through the 100-kOhm resistor instead of the 10-kOhm one based on the PRES equivalent diagram, not entirely sure. I may have to contact someone knowledgeable about the internal circuitry of the BQ40Z80. 

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    TI__Genius 9410 points

    Hi Luis,

    I will share the .gg file and additional details offline. Please note that the customer saw the same when using a volt meter, but using a scope they found the behavior described on my original post.

    Thanks,

    Antonio