BQ24780S: ACDRV/CMSRC resistor

Henry Kang

Part Number: BQ24780S

Hi Team,

bq24780s datasheet recommend to place a 4kohm resistor between CMSRC/ ACDRV pins and ACFET/RBFET for limiting current due to the ESD diode of these pins when turned on.

May i have your help to know how much is the lowest resistor that we can use?

over 6 years ago

0 Wang5577 over 6 years ago

TI__Guru 56650 points

Henry,

The resister value is depended on the resister power rating and input source voltage. For example: 0603 package and 19.5V input, the minimum resister value is 4kohm. Pdiss=19.5x19.5/4k=95mW. So, 0603 resister can survive.

0 Henry Kang over 6 years ago in reply to Wang5577

TI__Intellectual 1080 points

Hi Wang,
Thanks for your reply.
So there is no concern of resistance for the current limitation?
May i have your comment for the 2kohm with 1206 size(rating=0.25W)?

Thanks

0 Wang5577 over 6 years ago in reply to Henry Kang

TI__Guru 56650 points

Henry,

2kohm 1206 size is Ok to me.

BTW, with a reverse input, the 2kohm can survive. But, if the ACFET could be on with a reverse input. And then, several other pins (ACP/ACN; SW...) may get trouble. If you have reverse input concern, please add Q6, R12 and R13 as the datasheet application circuit.

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BQ24780S: ACDRV/CMSRC resistor