Other Parts Discussed in Thread: , TIDA-00883
The BQ40Z50 supports a very low quiescent current time-based shutdown mode, which is great for increasing shelf life of a battery.
Here's some info from the technical reference manual
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The bq40z50-R2 device can be configured to shut down after staying in SLEEP mode without communication for a preset time interval specified in Auto ShipTime.
Setting the PowerConfig[AUTO_SHIP_EN] = 1 enables this feature.
Any communication to the device restarts the timer. When the timer reaches Auto Ship Time , the time-based shutdown effectively triggers the MAC shutdown
command to start the shutdown sequence.
The bq40z50-R2 device returns to NORMAL mode when voltage at PACK pin > VSTARTUP
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I would like timed shutdown to be exited on a removable battery when the LED charge status display push-button is pressed.
This would allow checking charge status on a timed shutdown pack without requiring the pack to have a voltage applied externally to wake up the pack.
Looking at the schematic for the TI reference design at tida-00883, it appears there is an opportunity to use the LED pushbutton to turn on a P-MOSFET that would connect the BAT pin, through a 10K resistor + isolation diode to the PACK pin when the LED display pushbutton is pressed. This would allow "local wakeup" of a battery pack without the need for an external voltage to be applied. This would be valuable when checking the actual charge status of a battery that had entered timed shutdown.
One problem with this approach is finding a P-MOSFET with a low enough off state leakage current. For example, the BSS84 has a 15ua off state max leakage, which would not be good enough for the 2 meg ohm input impedance PACK pin of the BQ40Z50.
Any ideas on how to make the BQ40Z50 wake up from timed shutdown with the LED display button?
