BQ76930: Cell 3 value always 22mV, and cell 4 not read correctly

Hello Marsandhy,

Do you still have the Q7 MOSFET connected? This should not be placed if you are shorting the cell. Additionally, you may want to replace R30\R32 with 0-Ohm resistors. C7 should also be removed.

Best Regards,

Luis Hernandez Salomon

Dear Luiz,

i already remove some component as the picture, but the result still same

it's seem that the order of the measurement not correct after cell 3

Cell 5 value should be Cell 4, Cell 6 value should be Cell 5, but cell 8 value missing

Hello Mrsandhy,

At first glance it seems your connections are correct. Can you explain the order of measurements? Cell 4 is shorted, so it will always measure a lower voltage. How are you attaching the cells? 

Are you measuring with a voltmeter directly across the input pins/capacitor?

Best Regards,

Luis Hernandez Salomon

Hello Luiz,

i measure the voltage on the input connector, but i also check the voltage on the input pin capacitor the value is same.

Hello Marsandhy,

Are R2 and R4 populated? These shouldn't be populated.

It is hard to see if you have the filter components on the supply pins. Please reference to the picture above for key component connections. Also, this video walks around of how create your own schematic with the BQ769x0 family devices.



Note: Please ignore cell connections from VC10b and above as the BQ76930 only supports up to 10S.

Regards,
Jose Couso

Hello Jose,

R2 and R4 not populated,

i just follow this schematic reference from TI 

Hello Marsandhy,

1- What kind of diodes are being used for D11 and D12? These should be conventional diodes.

2- What if you attach all 10-cells? Do you still see the same issue?

3- Did you look at the video attached in my previous reply? The BAT and VC5x pins need filter components. 

4- Has the BQ76930 reported any fault conditions? 

These are common issues with reading cell-4 value:

• High impedance to the cells, particularly at the group boundary (since cell 4 connection to the cells includes VC5, VC5B and the VC5X power pin)
• Using a Schottky type diode 
• Unexpected short or open in the circuit
• Wrong component value (make sure all input pins have recommended RC filter values)

You can also reference to the image below for typical 7S bq76930 Configuration With External FETs. Note: Knowing the real component values is important.
This can also be found in SLUA810


Hopefully the above picture will assist you finding the issue.

Regards,
Jose Couso

Hello Jose,

1- What kind of diodes are being used for D11 and D12? These should be conventional diodes.

     --> I use 1N4148, also have tried with 1N4004 diode, the result still same

2- What if you attach all 10-cells? Do you still see the same issue?

     --> 10 cell configuration running well, all features also working (balancing, charging, discharge, etc)

3- Did you look at the video attached in my previous reply? The BAT and VC5x pins need filter components. 

     --> yes, i saw it, but i just follow this schematic, and i have checked the VC5X filter and already has (C5 and C11 on my schematic)

all component filter value already following the schematic above, on the schematic above the cap use 0.22uF

on the video the Cap filter value from 0.1 to 10uF

4- Has the BQ76930 reported any fault conditions? 

    --> UV_Trip

Regards,

Marsandhy

Hello Marsandhy,

Marsandhy Hariyanto said:

10 cell configuration running well, all features also working (balancing, charging, discharge, etc)

If the 10 cell configuration is working as expected, then something must not be connected right when going from 10S to 8S. 

To ensure that the shorted external FET circuitry is not causing this issue, please measure voltage across A-B and across C-D



Regards,
Jose Couso

Hello Jose,

voltage at AB is 3.282V and Voltage at CD is 3.282V

Vab

Vcd

Regards,

Marsandhy

Hello Marsandhy,

The multimeter readings seem right.

How are you reading the cell voltages? Are you using the companion gauge BQ78350 or are you using an MCU?

Using MCU:
Reading voltage issues can occur if the high and low bytes of the cell voltage are read in two separate transactions. Are you doing two I2C reads to read each byte? Reading both bytes together as a block read should fix the issue.

If using the BQ78350 as the microcontroller, make sure to select which cells are not being used.

Regards,
Jose Couso

Hello Jose,

How are you reading the cell voltages? Are you using the companion gauge BQ78350 or are you using an MCU?

--> I'm using MCU

Are you doing two I2C reads to read each byte? Reading both bytes together as a block read should fix the issue.

--> i read the value of each cell (2 byte) and looping it, and already tried also to read as block of total cell qty (8cells), the result is same

--> this is some of the codes

Regards,

Marsandhy

Hello Marsandhy,

Does the voltage you read on I2C matches the voltage you measured with the multimeter? 

Would you please refresh me the current issue you are experiencing? In the title of this thread cell-3 was reading low and cell-4 was reading incorrect, is this still happening? How are you confirming this?

What values do you expect to be reading? Can you please describe in details what issue you are seeing? 

Regards,
Jose Couso