BQ24040: Clarification regarding ISET2 and charge current?

Gregory Duperon

Expert 7430 points

Part Number: BQ24040

I have a question about the operation of the BQ24040 ISET2 pin.

My Setup:

ISET resistor = 2.2k (~250mA target charge current)

My Observed operation:

ISET2 = 0: charge current = ~250mA

ISET2 = float: charge current = ~100mA

ISET2 = high: charge current = ~250mA

From the datasheet, it appears that when ISET2 is floating or high, it operates independently of the ISET resistor. My observations would indicate that when ISET2 is high, the charge current is the lower of the ISET value or 500mA. Can you confirm that my observations match the expected operation of the device?

over 7 years ago

0 Bill Johns over 7 years ago

TI__Guru* 75656 points

Hello
This looks correct.
The ISET2 pin will limit input current
High = 500mA
Float = 100mA
Low= Iset
With an ISET value of 250mA you should get the above results.

Also see new application note SLUA901 on the BQ24040, it is a quick start guide to the device.

0 Gregory Duperon over 7 years ago in reply to Bill Johns

TI__Expert 7430 points

Hi Bill,

But, with ISET2 pulled high, charge current only appears to be ~250mA in my case.

So, are you saying, with ISET2 pulled high, my charge current should be 500mA? Thanks.

0 Bill Johns over 7 years ago in reply to Gregory Duperon

TI__Guru* 75656 points

Hi
The ISET resistor will set the output current, in this case 250mA.
Then ISET2 pin will set the max input current. For 500mA setting you only need 250mA of the available 500mA. For 100mA setting you will only get 100mA output current of the 250mA you are asking for.
With ISET2 low = ISET the input and output limits are the same.

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BQ24040: Clarification regarding ISET2 and charge current?