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BQ24193 HIZ mode

Jeff Lam55
Intellectual 420 points
Other Parts Discussed in Thread: BQ24193

Hi,

I have some questions related to BQ24193 charger which is used in our current design. 

Occasionally, if we leave our system power on overnight, the system may shut down with a drained battery in the morning (even with a USB power source plugged in).

A little more details with the setup/issue:

- USB charger is capable of providing over 1.5A.  

- System only consume under 700mA. 

- When the system is shut down with a drained battery, we notice no current is being drawn from the USB power source.

- This problem usually happens 8-9 hours after we have the system running but there are also other times that the system could continue to run over weekend without any issue

Our investigation and observations:

Below is a screenshot of the charger settings when we experience issue. We noticed that the charger was set to HIZ mode and the fast charge timer was set to 8 hrs.  If we unchecked enable HIZ, then the charger can charge again and everything is back to normal.

 

Questions:

1. We are very certain that our issue is related to the HIZ mode being enabled in the charger; however, we are unsure what triggered our charger to HIZ mode (safety timer or other reasons?).

2. If safety timer is what triggered HIZ mode, how come we can't reproduce this behavior consistently (some system could run over weekend without issue).

3. If HIZ is enabled after safety timer is expired, does the charger automatically disable HIZ to initiate a new charging cycle when Vbatt falls below the recharge threshold or we will need to manually clear HIZ register via I2C command?

4.  Any other recommendations or advice?

  • 0
    TI__Intellectual 1910 points

    Jeff,

    I agree that the battery drain is caused by the HiZ mode. Based on your description, the watchdog is probably expired and return charger to default mode (all values are reset to default). The safety timer behaviors differently in host or default as described in "Charging Safety Timer" section. The EN_HIZ is set high when safety timer expires and device in default mode. The EN_HIZ is clear when safety timer expires and device is in host mode.

    The ocassional reset to host mode may be related to how watchdog is reset to avoid expiration. If you have configured watchdog for 40s, we recommand to write to watchdog reset at least at half of the period such as < 20s or do two continous watchdog reset to ensure the device received the reset in case of i2c bit-error rate over a long period of usage.

    Hope this help.

  • 0 in reply to SamW2000
    TI__Intellectual 1910 points

    Here is a sanp shot of the datasheet for the behavior of safety timer describe.