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I'm currently designing a BMS that doesn't rely on a TI bq-series IC for gas gauging, protections, etc. So far, I have analog circuitry handling over and under-voltage cutoff, overcurrent cutoff, temperature cutoff, etc. Reference voltages are derived from the battery voltage using a voltage regulator. However, I've seen something referenced and I was wondering how it might be accomplished.

In many BMS systems, there is both a "sleep" mode and a "shutdown" mode. For example, in a datasheet for the bq28400:

When the bq28400 meets these conditions, the CHG, DSG, and ZVCHG FETs are turned off, and the integrated AFE is commanded to shut down. In Shutdown mode, the bq28400 is completely powered down because its supply is removed. To exit Shutdown mode the voltage at the PACK pin must be greater than the startup voltage specified in bq28400 datasheet. When this happens, the integrated AFE returns power to the bq28400 , the [WAKE] flag is set, and the integrated AFE is configured by the AGG. The [WAKE] flag is cleared and the [INIT] flag is set after approximately 1 s when all SBS parameters have been measured and updated.

This shutdown mode seems understandable; both the micro and the AFE are disconnected until a charge voltage is detected and is great enough. How would this charge voltage be determined sufficient to reconnect the AFE and bring the MC back online? Where would the reference for comparison be derived? It would be ideal to have this for long shelf-life, but I'm unsure as to how to accomplish it.

Here's the simplified block diagram of that bq-series for reference. bq28400 simplified block diagram

Thanks in advance guys

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