BQ76920: maximum discharge current with BQ76920

I'm not sure my question was answered, my question is, are there any limitations on the discharge current used to balance cells when using BQ76920?

With a 8 ohm resistor, given say 4.2V, in the worse case, a fully charged cell, the current flowing thru the discharge MOSFET would be around 550mA, for 4.2V that would be 2W of power dissipation on the external MOSFET. Can you tell me if BQ76920 can handle that? I can't see why not, it should really behave like a FET driver and an ADC and be flexible at that. If not, what other part can I use to replace BQ76920 with, which enables high discharge currents for balancing? I have 4 cells in series, so it has to work with as low as 4 cells.

Just to clarify, because of the ambiguous terminology, the discharge current here, is not the current flowing out of the battery pack, I understand that, and I understand the current sense resistor and the voltage drop across it depending on current, I'm not asking about that, I'm asking about the current that flows thru the cell balancing MOSFET, that is limited by a balancing resistor. In theory, BQ76920 should not care about that, however, in all your documentation, you are not using less than 20 ohm, and you are saying about not using less than 50 ohm, somewhere else, so I don't know if it's a limitation of the chip, or something else.

Hi Ion,

Just to clarify your question is regarding the balancing FETs not the CHG and DSG FETs. If so, then may i ask why you are not using the internal FETs in the bq76920? the bq76920 has capability to support 50mA of current internally for balancing, where you will only need to have a filter next to each channel pin (VCx) and the filter will give you the balancing current.

Thanks

Miguel

Thanks for the clarification. Typically, cell balancing happens during the charge cycle and in the tapering phase.

On the bq76920, the allowed MAX balancing current( without adding additional external circuitry for bypassing the high-currents) is  50mA.

please refer to SLUA749 application note for external balancing protection scheme with pFET and n-FETS.

In the above literature, it would be clear Cell_Discharge current = Balance current + Balance control current.  Typically the Balance control current is the

loop current that will flow thru the internal balance FET(inside of the bq76920, Rdsfet ~5  ohm).  The Balance current  will flow thru the  bypass FET.

hope this helps.