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BQ24070EVM: Removing and replacing battery while VIN is 5V - charging does not start when the battery is reinserted.

Jerry Molnar
Prodigy 140 points
Part Number: BQ24070EVM
Other Parts Discussed in Thread: BQ24070

Hi!

I'm using the BQ24070EVM board to validate our design.

At the moment the EVM is unmodified except for the addition of 2X 10uF caps from BAT+ to BAT-. These 2 are in parallel with the 10uF on the board, bringing
the total capacitance to ground equal to 30uF.

The battery is a single 18650 Li-Ion cell.

Instead of a wall adapter, the chip is powered by a lab supply set to 5V and the current limit is set to 1.25A.

JMP1 is set to 0.5
JMP2 is set to HI
JMP3 is set to EN

R_DPPM is set to 35.7K (TP1)
R_TMR is set to 50K (TP2)

All LED jumpers are installed.

There is a 20 ohm resistor connected from OUT to GND.

VIN is 5V

In "standard" operation the charging worked fine. It charged a drained battery nicely at a constant 1A until it tapered off and terminated the charging at a 100ma threshold.

Then I tried a few twists.

Partially charged battery. (Still taking 200ma of charging current).

[1] Remove the 5V input. Leave the battery in place. After a period of time, start up the 5V supply again.
All good.
The battery supplies the load current and when the 5V is powered up again, the charging resumes. (STAT1 LED on, STAT2 LED off).

[2] Starting with the 5V supply off and the battery removed. Insert the battery, and after a period of time, start up the 5V.
All good.
The battery is inserted, it is supplying the load current.
Then the 5V is turned on. Charging starts and the 5V supply is feeding the load current.

[3] Start with the 5V connected and the battery installed...Battery removal and replacement....(This test is to emulate a battery change in the field while the unit is powered on by the 5V).
Not working as expected.

Starts with normal charging operation as the 5V is on and the battery is installed.

Then the battery is removed.The 5V is always connected.

With the battery removed, the 5V supply is feeding the load current, as expected.

When the battery is reinstalled, STAT1 LED is off, STAT2 LED is on. No charging.

In order to get the charging to start up again (STAT1 LED on, STAT2 LED off), the 5V supply has to be turned off and on.


What do you think is happening is this case? Suggestions?

[4] Powering up the 5V with no battery installed.
Not working as desired.

Comes up in one of short circuit modes I think. Consuming 10ma from the 5V rail.
When the battery is connected, charging does not start. Still consuming 10mA.

What do you think is happening is this case? Suggestions?

Thanks and Best Regards
Jerry Molnar

  • 0
    TI__Mastermind 23885 points

    Hi Jerry, 

    Please see my comments below. 

    For scenario 3 what is the voltage of the battery when it is reinstalled? Additionally, can you check if charging will start up again if you change JMP3 from EN to DIS then back to EN? 

    For scenario 4 with no battery connected the device needs to be able to ramp up the output initially with no load attached due to the short circuit protection described on datasheet page 14. If you power up with 5V then connect the load at OUT the BQ24070 will be able to regulate at approx. 4.4V. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    Hi Garrett,

    Thanks for your replies.


    For the scenario 3 question, the battery was a pretty much fully charged battery...
    The voltage is 4.1V on the battery.
    When the battery is reinstalled and the system comes up with STAT1 LED off and STAT2 LED on, no charging, it does recover to charging when I disable the chip and then re-enable.
    That would work in our system.

    For the scenario 4 question, it did work as you described. With no battery and no load connected, the chip did come up and supplied the regulated 4.4V before and after the load was connected.
    That would work in our system.

    Kind of related to the scenario 4 question:

    I have another question about the capacitor from DPPM to GND which delays the onset of short-circuit protection.
    In section 8.3.5 it says the max value of that cap is 10nF.
    In 9.2.2.1 is says that this cap can go as high as 100nF.

    What are your thoughts about increasing the value beyond 10nF?

    Thanks
    Jerry

  • 0 in reply to Jerry Molnar
    TI__Mastermind 23885 points

    Hi Jerry, 

    Please see my comments below. 

    For scenario 3 the battery voltage being 4.1V is likely causing the BQ24070 to consider it fully charged. Toggling the charge enable forces the device to start a new charge cycle. 

    Good to hear you were able to replicate the same behavior in regards to scenario 4. 

    Jerry Molnar said:
    What are your thoughts about increasing the value beyond 10nF?

    I need to double check to confirm, but I believe the mention of as high as 100nF is incorrect. The recommendation should be to use no cap higher than 10nF. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    Hi Garrett,

    Thanks for your comments!That is very helpful.
    I'll wait to hear back from you re the 10nF vs 100nF cap on DPPM before closing off the issue from my end.

    Best Regards
    Jerry

  • 0 in reply to Jerry Molnar
    TI__Mastermind 23885 points

    Hi Jerry, 

    Thank you for your patience. Please see my comments below. 

    I have confirmed the recommended maximum capacitance to add to DPPM pin is 10 nF. This recommendation is due to the reasoning given in section 8.3.5 regarding how too large of capacitance will result in longer delay and increased risk of high currents if the output is in fact shorted to GND. 

    We will work to update section 9.2.2.1 to show 1 nF to 10 nF in the next datasheet revision. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    Hi Garrett,

    Thanks so much for your support! That is great.

    The part is perfect for our application and your support really helped.


    Best Regards
    Jerry Molnar