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BQ24072T: VBAT voltage switching on removed battery connection

Satoshi
Guru 19555 points
Part Number: BQ24072T

When bq24072T supply on disconnect battery (open) condition, VBAT occur nearly 2Hz switching.

※Ch1: Vin, Ch2: VBAT

Please let me know about three points below for above operate.

①I think that the reason is affect of safety timer signal from /CHG pin, correct?

②Is there way to reduce VBAT switching on disconnect battery condition?

　My idea is /CE set High, or disable safety timer (TRM to GND), I want to know the other idea and my idea correct or not.

　(If possible, I want to avoid /CE: High setting by keep in mind of total system setting.)

③About battery connect and disconnect on the same condition, is below setting no problem?

　・Over discharge (1.5V ~ 2.8V) to remove (0V)

　・Re-connect 1.9V battery

　・Connect the deep discharged battery: less than 1.5V

Best regards,

Satoshi

  • 0
    TI__Mastermind 23170 points

    Hi Satoshi,

    The waveform that you've provided looks to the battery detection routine that occurs when a battery is removed. You can see this in Figure 26 of the datasheet. You can set /CE high to disable this but will need to pull /CE when charging

    The charger will be able to charge a deeply depleted battery with a trickle charge. 

  • 0 in reply to Anthony P Pham
    Guru 19555 points

    Hi Anthony

    Thank you for reply,

    Sorry for additional question, please let me confirm two points below.

    ・When continue to battery removed (/CE: Low), is battery detection eternally switching?

    　Or, is there any timer and disable over time?

    ・When inserted 1.9V "deep depleted" battery, is it also operate trickle charge?  

    　I concern about VBAT(SC) described 2.0V_max, it may not leave battery detection routine.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Mastermind 23170 points

    Hi Satoshi,

    Satoshi said:
    When continue to battery removed (/CE: Low), is battery detection eternally switching?

    Yes, with the /CE pin low, the battery detection is still switching. There is no way to disable this but you can pull the /CE pin high to disable charging, which will disable the routine.

    Satoshi said:
    I concern about VBAT(SC) described 2.0V_max, it may not leave battery detection routine.

    Yes, this can be the case. If the VBAT does not remain above the VBAT(SC) value, it will continue to pulse, between the battery voltage and VBAT regulation, similar to the battery detection routine but also applying the fast charge current. In short, it fluctuates between fast charge state and battery detect due to short circuit.