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BQ79600-Q1: Clarification on INH Pin Functionality vs. NFAULT Pin in BQ79600-Q1

Burak GÜVELIOGLU
Prodigy 60 points
Part Number: BQ79600-Q1

Tool/software:

Hello,

I need some clarification regarding the functionality of the INH pin on the BQ79600-Q1, particularly in relation to the NFAULT pin.

From what I understand so far:

When the BQ79600 is in SHUTDOWN mode, and a fault occurs in one of the slave (stack) devices, the device detects a potential fault tone using the sniff detector.

If the tone is validated as a true fault, the BQ79600 transitions from SHUTDOWN to VALIDATE mode and activates the INH pin.

The INH pin is then used to wake up a PMIC, which in turn powers up the MCU.

However, I’m unclear about the difference between the INH pin and the NFAULT pin. Both seem to be fault-related, but:

Could you please clarify:

What is the exact role of the INH pin versus the NFAULT pin?

In which scenarios should each pin be used?

Can both be used together in a typical fault detection and wake-up system?

Can I connect the INH pin directly to one of the “wake-up” pins of the processor?

Thanks in advance for your support.

Best regards,

  • 0
    TI__Expert 6710 points

    Burak,

    Sorry for the delayed response.

    NFAULT is for the current device and only triggers whenever the FAULT_SUMMARY register of the BQ79600 is non-zero. It is also active-low, meaning that when a fault is detected the voltage on the pin is zero and when there is no fault detected the voltage on the pin is pulled to 3.3V. This is your default fault detection pin and should be used during normal operation. This pin is always low in VALIDATE mode.

    INH is specifically used for the scenario when you are using the Sniff Detector and Reverse Wakeup features of the device. It only goes high whenever the INH PMOS is activated and will stay high until it is specifically disabled even if the device is in SHUTDOWN. It is active-high and intended to drive the EN terminal of an MCU's power management, not directly attached to a pin in the processor, as it will be pulled up to BAT voltage. This is specifically useful when the stack devices are transmitting heartbeat tones to a BQ79600 in SHUTDOWN and you wish for the BQ79600 to enter VALIDATE mode. 

    Both pins are distinct and have their use cases. You should be using both in a typical system using reverse wake up.

    Regards,

    Bo