Using bq78PL114+bq76PL102 on 20 cells LifePo4 battery pack

The bq78PL114S12 is limited to 3 to 12 series cell operation.  Key points to consider.

PowerPump: It is not designed to balance beyond the 12th cell or below the first cell.  There really is no way to get around this without a product design change. 

SMBus:  The address for the device is fixed.  So if you have two PowerLAN gateways in your systems you would need a bus expander/level shifter circuit to talk to both.

Protection FETs:  Since the two 10 cell circuits would be in series, you would not want the lower one to have DSG and CHG FETs.  If they were to open, the battery would be split in half causing big problems.  Instead, use the DSG/CHG outputs of the bottom controller to drive the EFCIC/D inputs of the top controller.  This requires level shifting circuitry and logically ORs the control of the FETs.  The protection FETs would be associated with the top circuit. 

Current Sense:  Both should probably have sense resistors.  You may be able to get away with disabling the current sense of one however you will always be in the idle state which may present some problems depending on your application.

Jim

Hi Johann,

i think, there should be a solution to balance this 20 or more cells:

do an overlapping design, the cell 12 of the lower group is cell 1 of the upper group. Highest bq76pl102 of lower group controls FET for charge transfer down (south), bq78pl114s12 of upper group controls FET for charge transfer up (north). 

Oring of Safety as Jim mentioned.

Mirror the voltage of the shunt resistor to the upper bq78pl114s12

Reprogram the data address of the smbus data (if data-sheet is correct in this point)

Wear protective gear  ;-)

Regards

Andreas

The address can be changed but there are three points to note:

1. A customized .tmap file is needed to change the address.

2. The bqWizard 2.5.18 cannot communicate to a device without the default address.

3. The API does not communicate with a device other than the default address.

Hello Jim,

within SLUU330A i find:

"Extended SBData commands available for configuration and calibration, NDA required."

With this extended information, the API should not be necessary, changed address should work.

This information is also required if communication is done directly from a host to the chip via SMBus with new address or in system calibration or firmware upgrade is required without the possibility of the use of a GPIO USB Interface Adapter.

More information is required than this API contains which is edicted to the GPIO USB Interface Adapter.

• Is this extended information available?

Best regards

Andreas

NDA restrictions will be lifted for that information.  We are currently developing the documentation to allow users to directly access the bq78PL114S12 via a SMBus host controller (MSP430 or similar) much like the API does with Windows .NET and the USB-TO-GPIO adapter.

Thank you Jim!

That will give the flexibility required for development and production.

Best regards

Andreas

Hi Prierbert,

look into the product folder of bq78pl114, there you can download it.

Andreas

Andreas S said:

do an overlapping design, the cell 12 of the lower group is cell 1 of the upper group. Highest bq76pl102 of lower group controls FET for charge transfer down (south), bq78pl114s12 of upper group controls FET for charge transfer up (north). 

Mirror the voltage of the shunt resistor to the upper bq78pl114s12

Hi Andreas,

It is good idea, it can work up to 23cells.

How can be mirrored voltage between the two controllers? I thinking about switched capacitor and four FETs, but it is not good idea :-)

Regards Miroslav

A low power instrumentation amplifier like INA122 could provide this function.

Regards

Andreas

Hi all.  I've been reading over this products datasheet, really sounds GREAT and i really want to use it for my teams purposes.  I'm with Southern Illinois University Edwardsville Solar Car team.  We have Li-Poly battery pack that right now is 26 rows long (might change with the new world solar challenge restrictions) and I would love to use this product for this, but as Johann brought up, these chips only handle 12 in series.  So I would need 3 of these along with quite a few of the dual cell chips to do this.  Has anyone tried using multiple chips in series yet and been successful?  Would there be a better option? These seem almost perfect if they could be connected in series to handle far more then 12 at a time, obviously each chip could only keep track of their respective rows of batteries, but if a uC was placed as a bridge to gather info from each 8 or 9 cells and that data could be combined (mostly for reporting error conditions and state of charge) the only issue would be to balance the charge.   Any more thoughts on extending bq78PL114's abilities?  Thanks!

Dustin Sanders
Director - SIUe Solar Car Racing Team

Stacking each 12 cell BMS circuit consisting of 1 bq78PL114 and 4 bq76PL102s is possible.  Here are some quick thoughts about the possible implementation:

• They would be isolated from each other and they could not balance beyond the 12 cells that they are each connected to. 
• MOSFET control would have to be done by the top bq78PL114 and the lower bq78PL114s would need to drive the EFCI inputs of that top device through isolation circuitry.  This creates an And'ing of the MOSFET control.  You would only want one set of DSG/CHG/PRE MOSFETs.
• SMBus lines would need to be isolated. 
• Start by picturing the reference schematic in the datasheet stacked one upon the next.  What additional hardware would be needed?

Alternatively, we have a bq76PL536 device that is designed for monitoring groups of six cells and capable of high vertical stacking. 

Hi Jim,

we have the same problem. We need urgend access to the extende SMBcommands. Please contact me for bilateral NDA signment.

Regards,

Dirk

Hello，Jim

I have a project about bq78PL114EVM,and I need to use the Charge/Discharge SBD command  and the command of opening the balancing,how can I get these command?

Besides,Can I get the address of  Hardware Configuration Register and Algorithm Enable Register? It is very important for me.And I need them urgently.

Hi Yuxiao,

The following document provides guidance on how to access the SB commands for the bq78Pl116

http://www.ti.com/lit/an/slua591/slua591.pdf

Let me know if you have additional questions.

Regards,

Ben

Hi Ben,

the document slua591 is quite helpful, but its not really complete. Programming the extended SMBus Commands with the Pack Configuration Utility allow the user to access many information via dedicated SMBus commands. In our application we need a very tight control on the battery which means that we would like to access many parameters like cell voltages, OCV values, status register, alert register, and temperatures. Unfortunately the number of programmable SMBus commands is not sufficient to access als this information. We are sure that there is also the possibility to get these data with SMBus commands, like the BQWizard does. We would be very glad if you can provide this commands at least for the system parameters.

Regards,

Dirk

Hi Dirk,

The TRM Pages 55 thru 57 provides the extended SMBus commands and addresses.

http://www.ti.com/lit/ug/sluu481/sluu481.pdf

Hope this covers all the parameters you needed.

Regards,

Ben

Hi Ben,

thanks for your reply. Sluu481 does not answer my questions. We use already the extended SMbus commands to access as many parameter as possible. However we would like to read more values than adresses are available for extended SMbus commands. In addition to the parameter shown on page 56 and 56 of sluu481 we would like to read the OCV values of each cell as well as the alert registers. Of course these parameters are accessible via extended SMbus commands in principle, but there are not enough SMbus addresses to access all of them. Thats why we would like to access them as described in slua591 via adress 0x80 / 0x81. Unfortunately the commands for these values are missing.

Regards,

Dirk

Hi Dirk,

Please send to me you email address and I send to the File Access Protocol.

This document details how to access the additional commands you are requesting.

Regards,

Ben

Hi Ben,

how can I send you my email address? I don't have your one. In addition its in my settings so you should be able to contact me directly or via start conversation.

Thanks,

Dirk

Hi Benjamin,

i am also strongly interested in this file access protocol, could you send this also to me?

Thanks and best regards,

Andreas

Hello Andreas,

Do you get the information?

We are also here very interested by the subject!

Regards

Robert

Hello Robert,

no, for sure not. Also no answer nor comment.

The dismissive information politics for this product is strange and below all standards usually seen. Enjoy this special customer service at TI !

But we are on the way to make a reverse-engineering for the complete access and calibration protocol, if we finished, i'll post it here.

Regards

Andreas

Hi Andreas and Robert,

We did not want to post the File Access Protocol here since it is not full released.

You could send you email address to me thrugh the chat feature and I will forward the file preliminary file to you.

In the meantime, we are working on getting this document released to the web.

Thanks,

Ben

Hi Ben,

i am not familiar with the chat feature, so please send the preliminary file or contact data to: bq78pl114@googlemail.com

Thanks a lot

Andreas

Hi Andreas,

I sent the file to you on your fukuda address.

Regards,

Ben

Hi Ben,

that´s the best case. I am at home, so it was not possible to see incoming mails.

Regards

Andreas

Hi

 Ben,I have a project about bq78PL114,and I want to know  the File Access Protocol ,it is very important for me.This is my email address:

smalljade101@yahoo.com.cn

Thanks

Randy