BQ77915: BQ77915 Load and Charge current problem

Hi Alph, 

If both of the FETs are turning off, then you are having either a current fault or a temperature fault during discharge. In table 5 of our datasheet, we summarize the faults and the state of the FETs in that fault. You can use this table as a checklist to make sure none of these faults are occurring. Use the fault trigger conditions as a guide and measure the voltages of the respective pins. Hopefully, you will be able to narrow down the problem from this. 

Hi Shawn,

Thank you for your repply. But I did not the current problem still.   My circuit is 5S.

I looked at the table 5. I did not obtain conditions of this table. Vsrp-Vsrn value is normal in beginning at the load test. But after 20-30 second Vsrp-Vsrn value is going down. Then this is zero milivolt.

I checked all of circuits and Mosfets. I did not find any problem. 

I used 15 mili ohm and 7 mili ohm an 4 mili ohm and 2,5 mili ohm as RSENSE. 

Today I made a new card. But I did not get a good result unfortunately. May my BQ77915 be replica?

Is there another way out in your opinion?

Regards

Alph

Hi Shawn,

My BMS card was 5S.

I looked at table 5 but I did not solve my current problem. My bms card is not working good under the load for discharging.

I tried different Rsense value and I checked all circuit and especially Mosfets circuit but I did not find any problem on my card.

I measured Vsrp-Vsrn values. For example while RSENSE=4 miliohm Vsrp-Vsrn=-33 mV and after then 25 second Vsrp-Vsrn= 0 mV and CHG-DSG are turned off.

Today I made a new bq77915 BMS card with new components. But there is no solution still. 

I wonder if my BQ77915 is replica?

Do  you have solution suggestion?

Regards

Alph

Hi Shawn,

I looked table 5 but I did not find any solution for my problem. My bms card is 5S and very simple. 

Today I make a new BMS card with new bq77915 component but this card is not working under the load for discharge.

I there a new solution suggestion?

Thanks.

Alph

Hi Alph, 

Can you send me your schematic so that I can review it?

Hi, Shawn,

The schematic is attached.

Thank you.

Alph.BQ77915bms_ver2_sch.PDF

Hi Alph,

Nothing is standing out to me as being wrong on your schematic. So let's dig more into Rsns.

Do you see any change in the operation of the circuit when using those different Rsns values? Can you verify that faults occur at different currents for each of these resistors?

For choosing an Rsns value, refer to section 10.2.2.1 of the datasheet, in question 2. The Rsns value will change the current fault protection, so you want to make sure you choose the right value.

Hi Shawn,

I tried between 2 mili ohm and 50 mili ohm for Rsns resistor.

But I obtained maximum 1,19 Amper load current unfortunately. 

Above 1,19 amper, CHG and DSG FET drivers (either CHG or DSG) is turned off. 

I obtained maximum Vsrp-Vsrn=57 mili volts.

Sorry..

Regards

Alph.

Hi Alph,

Let's back up a little bit. For your application, what OCC and OCD do you need? From there, we will decide the correct Rsns value. Then you should be able to see the FETs turn off when those currents are obtained. 

Hi Shawn,

I need 10 Ampere for OCC and 22 Ampere for OCD.

Thanks and Regards,

Alph

Hi Alph,

I'm not sure you have previously specified what version of the BQ7715 you have. Is it the BQ7791500? This will determine the OCC and OCD voltage thresholds.

Hi Shawn,

My IC is only BQ77915  K86, not BQ7791500.

Regards,

Alph.

Hi Alph,

We have 4 versions of the BQ77915. They are BQ7791500, BQ7791501, BQ7791502, and BQ7791504. The EVM uses BQ7791500. Which one of these devices are you using?

Hi Shawn,

I understand but only  BQ77915 K8604 written on my IC. Is this IC replica?

Regards

Alph.