BQ24040: charging current does not fall down to 0A after \CHG pin turned to open drain

Chase Jeong

Mastermind 7345 points

Part Number: BQ24040

Hello TI experts,

about 1 month ago I asked about the review of the BQ24040 schematic;

https://e2e.ti.com/support/power-management/f/power-management-forum/983721/bq24040-please-review-the-schematic

now they made their own PCB and test it.

and we checked that the charge current is 790mA and termination current is 59mA.

we saw that \CHG pin turned to open drain around 59mA.

the problem is, i expected that charging current would be fall to 0A right away after \CHG pin turned to open drain.

(please see figure 8.1 in datasheet.)

but the charging current is still about 59mA, and it decreased slightly down until it reaches to 0A.

and we saw this in EVM too.

is it normal operation? or do we something wrong?

please check this issue. Thanks.

Best regards,

Chase

over 4 years ago

0 Nick Brylski over 4 years ago

TI__Mastermind 19195 points

Hi Chase,

Do you have some waveform to show this? There is some tolerance with when this CHG pin will be triggered I wouldn't expect it to be to significant.

Thanks,

Nick

0 Chase Jeong over 4 years ago in reply to Nick Brylski

Mastermind 7345 points

Hi Nick,

Here is waveforms which you can refer, but this is not the result of the test above ;

x axis is the time(hour).

there is no point falling down to 0A clearly.

please check this issue. Thanks.

Best regards,

Chase

0 Nick Brylski over 4 years ago in reply to Chase Jeong

TI__Mastermind 19195 points

Hello Chase,

The IC will slowly taper current until it reaches the termination current.

Best regards,

Nick

0 Chase Jeong over 4 years ago in reply to Nick Brylski

Mastermind 7345 points

Hello Nick,

Yes I understand what you said.

and, how about after reaching termination current? I think it is normal operation that it falls to almost 0V after it reaches the termination current.

but i cannot see the falling current to 0V in the log above.

can you explain it more?

Best regards,

Chase

0 Nick Brylski over 4 years ago in reply to Chase Jeong

TI__Mastermind 19195 points

Hi Chase,

In your log it looks like the current never reaches 59mA. This is the point where termination reaches and current should drop to zero.

Best regards,

Nick

0 Chase Jeong over 4 years ago in reply to Nick Brylski

Mastermind 7345 points

Hi Nick,

my customer tested again, here is the updated log;

fast charge current is about 700mA, termination current is set to 30% (6.2Kohm)

I think it would fall to about 200mA to 0A, but it felt to 0A when it reaches 100mA.

is it normal operation for this situation?

and I have one more question,

it does not fall to 0A clearly, suddenly 110mA appeared, and 20mA is minimum charging current. not 0A.

i will also attach a log for you.

li-ion 1400 charging Test.xlsx

Please check this issue. Thanks.

Best regards,

Chase

0 Nick Brylski over 4 years ago in reply to Chase Jeong

TI__Mastermind 19195 points

Hi Chase,

Can you attach the schematic for review.

Thanks,

Nick

0 Chase Jeong over 4 years ago in reply to Nick Brylski

Mastermind 7345 points

Hi Nick,

Here is the latest schematic. please check it. Thanks.

Best regards,

Chase

0 Nick Brylski over 4 years ago in reply to Chase Jeong

TI__Mastermind 19195 points

Hello Chase,

With the TS pin pulled up to 5V the part will be in TTDM and termination is disabled.

Also note any current delivered by the OUT pin is used to determine when the device reaches the Termination point. If you have a load connected to the battery this could also influence the results.

Best regards,

Nick

0 Chase Jeong over 4 years ago in reply to Nick Brylski

Mastermind 7345 points

Hi Nick,

Thank you for your support.

- customer does not have any load on output.

- and I checked that if TS pin is pulled to high termination is disabled.

and i have one question, customer finally decided not using thermistor, so they connected TS to VSS through 10kohm. but they checked that IC seems alive but cannot start charging. can you guess what is the reason for this?

Best regards,

Chase

0 Nick Brylski over 4 years ago in reply to Chase Jeong

TI__Mastermind 19195 points

Hello Chase,

In what conditions is the device not charging? How is this being tested and at what battery voltage?

Thanks,

Nick

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BQ24040: charging current does not fall down to 0A after \CHG pin turned to open drain