TIDA-01093: I2C Communication

Hello Rohit,

How often does this happen? If you measure the actual cell voltages, do they match with what the evaluation software is showing? Does this occur at all times, or does it occur in cases like cell balancing?

If you are using TIDA-01093 as reference, is this intended to be used as a stacked configuration? If using 10s, TIDA-00449 may be more helpful. 

Can you share your schematic to make sure everything is okay?

Best Regards,

Luis Hernandez Salomon

Luis it happens frequently while load connected or not irrespective to it , cell voltages changes randomly in a group of 3 adjacent cells only.

Yes they do match with evaluation software as well.

It happens even when cell balancing is not happening,

In personal message will share you the schematic.

it happens in all freshly built Pcb's or BMS. Out of 10 all went incorrect.

Rohit

Hello Rohit,

I checked your schematic. It seems okay at a first glance. How are you shorting it to make 8s? For 8s you want to short VC4–VC3 and VC9–VC8, as mentioned in Table 25. Cell Connections for bq76930 in the datasheet.

Short starting from the upper IC. How often does this behavior occur? Are you able to see normal readings at any time? Which group shows the abnormal behavior? It is odd for this to show up randomly. Keep in mind that the evaluation software was not made with a stacked device in mind.

Are you reducing the cell count for both ICs? Do you see the same behavior on the top and bottom IC?

Best Regards,

Luis Hernandez salomon

Yes luis, 

For shorting am following as per datasheet for both afe's.

As per Vc4-Vc4 and Vc8-Vc9 to make 16s.

Yes for eval software am connecting at a time single afe only and reading volt. 

This behaviour repeats randomly any time. Yes for sure at times it works perfectly.. 

Yes behaviour repeats for both top and bottom. 

Rohit

Hello Rohit,

Do you have an MCU controlling the BQ76940s? 

I will ask with the team to see if they have an additional thoughts on this. 

Best Regards,

Luis Hernandez Salomon

Hello Rohit,

Is the stack voltage adding up to the right voltage?

Can you check your wire connections, it may be that the cell connections into the IC may not be strong enough and it is creating an open-cell scenario.

Best Regards,

Luis Hernandez Salomon

Yes, wire was dry. 

But  one thing I observed is , when dry wire, capacitor charges to max unstable voltage, and same survives, long, even when afe put in to ship mode. 

For eg if max fluctuatuon recieved is 6 volt momentary, same voltagw stays for long, which causes balance frts to turn on, unexpectedly 

Can you share more improvements? 

Rohit

Ok luis, 

But y does capacitor picks up at times max voltage spike and remains at same level for long, which will cause incorrect reading by afe. 

Rohit

Hello Rohit,

Is this happening due to poor connections? Each capacitors should be around the cell voltage. If you are seeing these weird voltages, again check that every connection is strongly done.

Best Regards,

Luis Hernandez Salomon