BQ24721C: Differences case between AC adapter detect comparator (ACDET) in practice and datasheet

MIKE MIKE

Part Number: BQ24721C

Dear TI Engineer,

I have an output voltage of 18V and when the voltage drops to 15.1V（VACDET<=1.2V）the BQ24721 determines that the AC adapter voltage is unstable and switches off the ACFET via ACDRV within 1us.

Of course, adding a slow ON capacitor to the ACDRV would be another case.

This is also mentioned in the Datasheet, see the marked pictures below:

However, in practice I found that the time marked in the Datasheet for the AC adapter not detected deglitch time does not match the time I actually used.

My question is: When I break the connection between the ACDRV and the MOSFET´s gate, what is the actual enable time of the ACDRV?
I measured it to be much greater than 1 microsecond and up to millisecond. Is the Datasheet incorrectly, or is there some mistake in the way I am testing?

Please feel free to ask any questions if you are not understand or not clear.

over 3 years ago

0 MIKE MIKE over 3 years ago

Prodigy 10 points

hi TI expert,

is there any response for this question? your fast response is very appreciated, thanks

0 MIKE MIKE over 3 years ago in reply to MIKE MIKE

Prodigy 10 points

queries to TI.rtf

0 Angelo Zhang87 over 3 years ago in reply to MIKE MIKE

TI__Genius 11850 points

Hi Mike,

Unfortunately, the BQ24721C is a very old device, and we don't have an EVM to test this on the bench. Can you capture an oscilloscope waveform showing VCC, ACDET, and /ACDRV on the same graph as you unplug the adapter? Please trigger the waveform on the falling edge of ACDET so we can see how long it takes /ACDRV to respond.

Best regards,

Angelo

0 MIKE MIKE over 3 years ago in reply to Angelo Zhang87

Prodigy 10 points

hi Angel,

we measured three signals, see it in attachment

Reply to TI 202107101107.docx

0 MIKE MIKE over 3 years ago in reply to MIKE MIKE

Prodigy 10 points

hi Angelo,

sorry to interrupt your weekend, we are very pleased to see your fast response.

0 MIKE MIKE over 3 years ago in reply to Angelo Zhang87

Prodigy 10 points

Hi Angelo,

could you help check it as soon as possible?Sorry that we have the problem of production line down, thanks

0 Angelo Zhang87 over 3 years ago in reply to MIKE MIKE

TI__Genius 11850 points

Hi Mike,

Thanks for the waveforms. When you unplug the adapter, the input voltage and ACDET falling slew rate is very slow in the waveforms. Is it possible to decrease the input capacitance so that the fall time is faster? Alternatively, you can try manually shorting ACDET to GND while the adapter is already inserted. A faster fall time should provide a more accurate measurement of the /ACDRV response time.

Best regards,

Angelo

0 MIKE MIKE over 3 years ago in reply to Angelo Zhang87

Prodigy 10 points

Hi Andelo,

the input voltage is determined by our board which capacitors cannot be removed, And there’s no capacitor short to ACDET, we are not trying to speed up the falling time, but to confirm with you the current falling time shown in waveform is accepted, could you confirm it? Thanks

By the way, we will provide the test data according to your comment, is there additional information to be added?

0 MIKE MIKE over 3 years ago in reply to Angelo Zhang87

Prodigy 10 points

HI Andelo, I manually shorting ACDET to GND, a faster fall time on ACDET with falling edge trigger graph attached. My conclusion is the deglitch time of adapter not detect until the /ACDRV response is fixed. That is 8ms.

Reply to TI 202107130954.docx

0 MIKE MIKE over 3 years ago in reply to MIKE MIKE

Prodigy 10 points

hi Andeko，
Any comment?

0 Angelo Zhang87 over 3 years ago in reply to MIKE MIKE

TI__Genius 11850 points

Hi Mike,

Based on your waveforms, your test results seem accurate (8 ms until /ACDRV is pulled high). I think the 1 us typical ACDET falling deglitch time in the EC table only refers to the response time of the ACDET comparator itself. However, there is additional propagation delay through other internal logic circuits before /ACDRV is pulled high, which contributes to the total /ACDRV response time of 8 ms that you measured.

Best regards,

Angelo

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BQ24721C: Differences case between AC adapter detect comparator (ACDET) in practice and datasheet