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BQ25628: BQ25628 unable to cut off VSYS during ship-mode

Taspon Gonggiatgul
Prodigy 30 points
Part Number: BQ25628

Tool/software:

Hi,

I am currently running into an issue in my design where triggering ship-mode does not completely off VSYS. My current setup uses 4.2V linear PSU output as VBAT (no charging). When ship mode is entered via I2C commands, VSYS drops down from 4.2V to 3.8V instead shutting off completely. Under this case, my MCU ended up being still powered and reading VBAT and IBAT via the ADC registers all results in 0 reading. However, Reading the charger status register 0x1D gives me 0x11 (both the VSYS_STAT and WD_STAT fields are set to 1), which seems very strange to me.

Overall, I believe the ship mode command is indeed doing something, but at the same time I don't quite understand why this doesn't completely shut off my BATFET. Any help or suggestion would be greatly appreciated. Thanks!

Best,
Taspon

  • 0
    TI__Mastermind 31800 points

    Hi Taspon, 

    Thank you for reaching out via E2E. Please see my comments below. 

    Firstly, below is a waveform I captured entering shipmode on the BQ25628EVM with a 50mA load at SYS. When shipmode is entered path from battery to SYS is shut off and VSYS voltage should continue to decay (unless you have some external power path to SYS rail). 

    Additionally, in ship mode I2C functionality on the BQ25628 is turned off. Even if MCU remains powered expectation is all I2C transaction attempts to the BQ25628 will NACK. Given your observation that you can read from REG0x1D it would appear your device is not actually in ship mode. I recommend you check to make sure you are not accidently exiting shipmode via either driving QON pin low or connecting an input source at VBUS. 

    Best Regards,

    Garrett