BQ25798: BQ25798 Charge Balancing

Carl Olen

Part Number: BQ25798
Other Parts Discussed in Thread: BQ40Z50, , EV2400

For 2s, 3s and 4s battery configurations, how does the BQ25798 manage charge balancing such that each cell's voltage is balanced?

over 4 years ago

0 Jeff F over 4 years ago

TI__Guru**** 165886 points

Hi Carl,

The BQ25798 does not provide cell balancing. You will need a separate IC that performs that function.

Regards,

Jeff

0 Carl Olen over 4 years ago in reply to Jeff F

Expert 1160 points

That's what I thought, when I saw nothing about that in the bq25798 datasheet. I'm looking to charge and balance two 18650 Li-Ion batteries in a 2S configuration. What separate IC do you recommend that would go with the bq25798? I would like to get something that could do 3S or 4S as well, for other projects. Please let me know. Thanks, Carl

0 Jeff F over 4 years ago in reply to Carl Olen

TI__Guru**** 165886 points

HI Carl,

Try BQ40Z50. I don't support that part but it seems popular.

Regards,

Jeff

0 Carl Olen over 4 years ago in reply to Jeff F

Expert 1160 points

Jeff, thanks. Do you have an example application or a couple of reference designs where the bq25798 and bq40z50 are used together?

0 Jeff F over 4 years ago in reply to Carl Olen

TI__Guru**** 165886 points

Hi Carl,

There is no reference design with the 798. It is too new. I have forwarded to a coworker who is more familiar with the gauge and balancing ICs. Hopefully he can direct us to a reference design with another charger and possibly a better option for balancing IC.

Regards,

Jeff

0 Carl Olen over 4 years ago in reply to Jeff F

Expert 1160 points

Jeff, okay. I'll wait to hear back from your co-worker. Thanks, Carl

0 Wyatt Keller over 4 years ago in reply to Carl Olen

TI__Guru** 105590 points

Hello Carl,

There's no specific reference design that uses them both together, essentially what you would do it connect PACK- on the gauge to the PGND on the charger and PACK+ to BAT. I attached a very simple block diagram for the connections.

After the battery is fully learned (SLUA903) you can set the balancing to be enabled and the gauge will perform passive cell balancing as described in section 7.1 of the TRM https://www.ti.com/lit/pdf/sluua43

The TRM is the best source of information for cell balancing using the gauge.

Sincerely,

Wyatt Keller

0 Carl Olen over 4 years ago in reply to Wyatt Keller

Expert 1160 points

Thank you Jeff and Wyatt, I will give this a try and let you know how it turns out.

0 Carl Olen over 4 years ago in reply to Wyatt Keller

Expert 1160 points

Wyatt, I don't see where the bq25798EVM has SMBC and SMBD connections. I do see the I2C connections for SCL and SDA. Is that what should be connected to the bq40z50EVM's SMBC and SMBD connections, respectively?

Carl

+1 Wyatt Keller over 4 years ago in reply to Carl Olen

TI__Guru** 105590 points

Hello Carl,

Yes the BQ25798 uses I2C, the diagram I shared is for a similar setup, all the connections should be the same besides the names. SCL = SMBC, SDA = SMBD is correct.

Sincerely,

Wyatt Keller

0 Carl Olen over 4 years ago in reply to Wyatt Keller

Expert 1160 points

To which bus on the EV2400 should I daisy-chain this connection, I2C (Port 2) or SMB (Port 1)?

0 Jeff F over 4 years ago in reply to Carl Olen

TI__Guru**** 165886 points

Hi Carl,

SMB Port 1.

Regards,

Jeff

0 Carl Olen over 4 years ago in reply to Jeff F

Expert 1160 points

Thanks, Carl

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BQ25798: BQ25798 Charge Balancing