BQ2970: Implementation with Samsung Q30 cells

Hi Power,

You might discuss restrictions with the cell supplier, they may have other information not in the data sheet. 

BQ2970 does have zero volt charging, it has a 0-V charge inhibit voltage but it is low, see the data sheet, it would not meet the 2.3V limit your note.  BQ2982 has zero volt charging disable, but again the thresholds to disable the charging by the charge pump are below the 2.3V limit you note.  

Thank you for the reply.

After additional research, I found that the cell allows charging from 1v (at 0.1C). This is good news, however the devices that support 0V charging have their threshold at 0.75v

This 1v precharge threshold seems to be shared between Samsung and Sony, and maybe other popular manufacturers for high-reliability cells.

The question is, which cells were these BMS devices designed for? Why 0.75v? And are there other BMS devices that are designed for 1v?

Hi Power,

The part specifications appear to describe where the 0-V charge feature works leaving the choice of where 0-V charging should not be used on the system to the charger. So the part always supports 0-V charging for a cell which allows it to 1V rather than enforcing a limit of 1V (or a selectable limit) on a cell.

The BQ2982 has the feature disabled, again it has fixed thresholds.  I'm not aware of a part with selectable 0-V charge disable threshold.

I have read through the datasheet that includes the BQ2982 - its Overcharge threshold is 4.4v, and I am not aware of any Li-Ion chemistry that supports that. Do you have a suggestion of a cell that works with this device?

Additionally, I have checked with our suppliers and none have this device in stock - in fact, they don't have it in their catalogue either. Is it in production at all?

Thank you.

Hi,

Apologies for the delay, we have been on holiday here in the US.

We create several different configurations with different thresholds for different battery packs. We recommend choosing the battery cell that works for your system, then choosing the appropriate protector. We do not typically recommend battery cells.

You should be able to expect the BQ2982 to be in stock later this year.

Hi Shawn!

You are 100% correct, of course. And this is what we did. But I cannot for the life of me figure out why there is no single-cell BMS+Charger configuration offered for most of the 18650 Power Cell catalogue of both Samsung and LG.

The datasheets state Operating Voltage 4.2v ~ 2.5v. The cells allow overcharge to about 4.3v with no safety hazards, and allow precharging from 1v to 2.5v at 0.1C or 0.5C in a temperature-regulated environment. These numbers are true for 90% of all Li-Ion cells that I have ever came across. And I find it very hard to believe there is no BMS + Charger config that supports this.

So I'm trying to find out what am I missing. Again, the 2982 resolves the overdischarge issue but allows charging to a voltage that is too high for most 18650 chemistries.