BQ2980: 2S and 3S alternatives with hibernate and cell balancing

HI Dan,
Thank you for your interest in our protection ICs. Please find below my feedback.

1)
I can see that BQ77915 implements a similar hibernate feature for 3-5 cells.
Will the protection features of the BQ77915 still work for the 3Sx6 configuration illustrated above? e.g. with parallel cells.

[David Hien - 2020-01-10]yes. Many (all?) of our customers use our parts with parallel cells

2)
If we decide to go with a 2Sx6 configuration, is there another alternative Battery Protector that will allow us to keep the hibernate and balancing features?

[David Hien - 2020-01-10]we do not have a 2s protector IC with the features you mentioned above

3)
The above questions treat each parallel row as a single cell and connect to the Battery Protector as though it were just a simple 2S or 3S configuration.
How can we implement protection on an individual cell level? I’m not sure if it is necessary, but this E2E thread implies that it is.

[David Hien - 2020-01-10]I do not think that it is necessary. I'll check or pass your question along.

BQ77915 provides passive cell balancing. Is it possible to implement active balancing for the 3Sx6 and 2Sx6 configurations?

[David Hien - 2020-01-10]we do not have recent devices with active cell balancing. We have a recent training video here about active cell balancing with some part info.

Hi Dan,

I'm glad you like the BQ2980! As for your questions:

1. Yes I would suggest the BQ77915 for this application. You are correct, it will see the the parallel cells as one single cell. This is also true for the rest of our devices.
2. For 2S, your best bet will probably be the BQ2920X family. This product family also supports cell balancing. It does not have a hibernate mode, like the BQ77915, but it does have an Icc of less than 3 uA. The datasheet can be found here:
   1. 1. http://www.ti.com/lit/ds/symlink/bq29200.pdf
         
3. I agree with my colleagues on this one. Our devices are not able to monitor the individual cells (unless it was a nS x 1 configuration). 
4. Here is a video that describes the cell balancing features of the https://training.ti.com/how-cell-balancing-feature-works-bq77915. You can configure the Vstep to balance more often, but it is not possible to have the device balance at all times. 

Thanks David and Shawn. That was very helpful.

2) a.
If testing shows that we need to use the 2Sx6 configuration, is it possible to implement the hibernate feature with discretes or another IC between the Battery Protector and the cells or the charge/discharge FETs?

2) b.
We can’t give up the hibernate feature because we use it for too many things. Low power consumption is great but we like the hibernate feature because it opens the FETs and removes the load from the batteries until the next charge.
Are there any other Battery Protectors that have this feature with other cell configurations?
Can we somehow daisy chain the BQ2980?

4)
Your battery protectors don’t provide active balancing, but do any of your dedicated battery balancers?
Can they be implemented between the Battery Protector (BQ77915 or 2S version) and the cells?
http://www.ti.com/power-management/battery-management/monitors-balancers/products.html#p2192=Cell%20Balancing&sort=p1152min;asc

Kind regards,

Hi Dan,

Unfortunately, there are not any devices that support 2S with the required features you mention. With a 3S configuration, you will have better options and I think the BQ77915 would work well in this case. You can also look at the BQ28Z610 for the 2S case, but I think this will likely be overkill since it is a much more complex device (integrated battery gauge with protection and cell balancing). 

As far as daisy chaining the BQ2980, this may be possible but I have not seen this attempted before.

Active balancing tends to be expensive to implement and we do not see it used in most applications. There are a couple of TI devices that support active balancing. Here is a video on that topic: https://training.ti.com/demonstration-16-channel-active-cell-balance-solution. Most TI battery ICs use passive balancing.

Best regards,

Matt

Thanks Matt,

Overkill is ok. I need to add a high speed battery gauge, OTG charger and a wireless charging interface. I just assumed that these would all be individual ICs like they were in a previous 1S design. BQ28Z610 doesn't appear to have the hibernate feature so 3S still seems better with regards to which battery protection IC we need.

The decision on whether we use 2S or 3S will be made based on component availability. The protection and charger ICs indicate that 3S is best. However, I'm struggling with the USB OTG charger and the wireless charging interface which is why I would like to keep the 2S option open. But that's probably a discussion that should be started in another post.

Can the EMB1428Q and EMB1499Q (from the 16-Channel Active Cell Balance Reference Design) be used with the BQ77915 for active balancing? It seems that the EMB1428Q is TI's only active balancing option.

Kind regards,

Hi Dan,

If gauging is needed, then there might be a couple more different options. The EMB1428Q and EMB1499Q devices would not work with the BQ77915 because they need voltage measurements so that balancing decisions can be made by an MCU and the BQ77915 does not provide these.

The BQ4050 or BQ40z50 (1-4 cell battery gauges) might be able to work with EMB1428Q or EMB1499Q since they provide very accurate voltage readings. These devices have Sleep and Shutdown modes with lower current than the BQ28Z610. The main difference between the BQ4050 and BQ40z50 is the gauging algorithm. The BQ40z50 has the best potential accuracy since it uses Impedance Track, but the CEDV algorithm used by BQ4050 may be a little easier for a first time user and may be the better choice is you have high-pulsed current loads in your application. 

Regards,

Matt

Thanks so much Matt.

BQ4050 and BQ40z50 might be perfect for what we need!

Hibernation

The Emergency Shutdown feature on page 24 of either datasheet (https://www.ti.com/lit/ds/symlink/bq4050.pdf#page=24) is close to what we are looking for but we need to shut everything down from the MCU, or if there is a fault, directly from the protection IC.

Then we need to wake up the protection IC and the rest of the system with the charger which will most likely be either BQ25710, BQ25713 or BQ25713B because of their OTG capabilities (I'm discussing that here: https://e2e.ti.com/support/power-management/f/196/t/872417)

It looks like the MCU can force BQ4050 or BQ40z50 into Hibernate (Emergency Shutdown) by driving the SHUTDN pin low from a high state. However, in order to recover the system, the charger would need to pull the SHUTDN pin high and then drive it low again. It seems like the SHUTDN pin is designed to be used with a reset supervisor IC but that just adds more quiescent current.

Is there a better way to achieve wake up on charge?

EDIT: It looks like the ManufacturerAccess() MAC Shutdown feature will do exactly this. Can you please confirm?
Section 5.4.2 on page 41 - http://www.ti.com/lit/ug/sluuaq3/sluuaq3.pdf#page=41 
That Technical Reference manual is for BQ4050, but does it also apply to BQ40z50?

System Present vs Shutdown

The SHUTDN and PRES features share a pin. How do we select which feature we want to use? I couldn't find it in the datasheet.

Do we need the SHUTDN feature enabled (System Present disabled) in order to use the ManufacturerAccess() MAC Shutdown feature, or is that a separate thing?

Active Balancing

Can the included balancing be disabled (if not done automatically) when the BQ4050 or BQ40z50 are in hibernation?

Would BQ4050 or BQ40z50 even need EMB1428Q or EMB1499Q for active balancing?
It seems like active balancing is already included.

"Reduces the charge difference of the battery cells in fully charged state of the battery pack gradually using a voltage-based cell balancing algorithm during charging. A voltage threshold can be set up for cell balancing to be active. This prevents fully charged cells from overcharging and causing excessive degradation and also increases the usable pack energy by preventing premature charge termination." https://www.ti.com/lit/ds/symlink/bq4050.pdf#page=24

If they don't need EMB1428Q or EMB1499Q then how would you wire the active balancing?

Typical Application

Why do both BQ4050 and BQ40z50 need the BQ2947 added when they already have overvoltage protection and monitoring included?
Page 28 of either datasheet - https://www.ti.com/lit/ds/symlink/bq4050.pdf#page=28

BQ2947 wouldn't be disabled when the BQ4050 or BQ40z50 are in hibernation. Is this chip necessary?

Kind regards,

Thanks Matt,

That was very helpful.

I've continued the thread here:

Kind regards,