BQ24075T: bq24075T / Reverse current after input removed

S.Satoshi

Part Number: BQ24075T

Hi,

Now my customer is evaluating bq24075T EVM and confirm the behavior when input voltage is removed. In this case they add discharge resistor between IN and GND. Then they can see reverse current for approx. 20msec after input voltage is removed. I'd like to know this is expected behavior of bq24075T or not. This can be seen on EVM so can you try to duplicate it and give your opinion?

Best Regards,

Satoshi / Japan Disty

over 8 years ago

0 Kerry Song over 8 years ago

TI__Intellectual 1980 points

Hello

The current waveform is IBAT, IIN or Iout? You mean you connect a R before VIN pin ,what's the reason?

0 S.Satoshi over 8 years ago in reply to Kerry Song

Guru 21685 points

Hi Kerry,

The current waveform is input current. This shows positive current but I measured current from IN pin to discharge resistor, so this means reverse current.

The purpose of this this charge resistor is to discharge input capacitor immediately after input source is removed.

Best Regards,

Satoshi

0 S.Satoshi over 8 years ago in reply to S.Satoshi

Guru 21685 points

Hi Kerry,

I believe that you can see this behavior by using EVM on your bench. So please try this.
Best Regards,

Satoshi

0 Kerry Song over 8 years ago in reply to S.Satoshi

TI__Intellectual 1980 points

Hello

I understand your issue. OK, I will test it for you tomorrow.

Regards

0 Kerry Song over 8 years ago in reply to Kerry Song

TI__Intellectual 1980 points

Hello,

What's your position of current probe, could you check is it the discharge current of CIN?
meanwhile, what's the value of RIN and CIN. could you give me your connection information(SCH) of discharge resistor, I need to know it's position.

0 S.Satoshi over 8 years ago in reply to Kerry Song

Guru 21685 points

Hi Kerry,

Thank you for your support. Please see attached for schematic and test point. It also includes the test result I measured by using EVM with default external components. Then I couldn't see constant reverse current like previous result that reported from my customer by using EVM.

So can you please test by referring my test condition?

bq24079TEVM Input current at Vin removed.pdf

Best Regards,

Satoshi

0 Kerry Song over 8 years ago in reply to S.Satoshi

TI__Intellectual 1980 points

Hello,

Don't recommend that add a resistor to discharge input capacitor immediately after input source is removed. The resistor is not needed for our IC.

From your waveform, I can see that the diverse current is instantaneous, so we can conclude that the MOS between VIN and OUT pin is normal, MOS is off when VIN plug out. And your current test point is between cap and resistor, it may be the discharge current of your cap.

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BQ24075T: bq24075T / Reverse current after input removed