BQ76940: BQ7694001+bq78350-r1

Hi Alexander,

from the description seems, the REGOUT is shutting down when the device is going into SLEEP. Have noted such problems, if the middle and the upper groups

CAP2 and CAP3 retain residual voltage. how much capacitance is on  CAP2 and CAP3.

Try connecting a bleed resistor(~1M) on CAP2/VC5X, similarly 1M on CAP3/VC10X. then try the same sequence.

also check, if there is pullup on SCK/SDAT(5K-7K)?

hope this helps out...

 

Hi Vish ,

I tried your recommendation :

1. bleed resistor(~1M) on CAP2/VC5X, similarly 1M on CAP3/VC10X. --> I connected parallel 1Mohm resistor to 1uF Capacitor on CAP2 and CAP3 .
2. there is pullup on SCK/SDAT(5K-7K) --> I changed from 10K to 5.9Kohm.

The result is the same , it enters to shutdown correctly , but problem on wake up from Shutdown according to picture above !

Please check what additional i should do to repair this issue .

B.R Alex Burtakov

Hi Alex,

any update on this resolution. Seems both DSG and CHG are OFF and indicating the XREADY is active. Clear the  STATUS register by writing all 1s.

Hi Alexander,
I cannot exactly reproduce your experience.
Your picture does not show the "scan" active so the data displayed may be from a one time read. You might try to do a "refresh" or set "scan" for continuous register updates after re-booting.
When I have seen the display of ffff... on the bq78350 identification on the dashboard it is because the bqStudio has become confused. For me the register area will continue to update properly with scan selected. I don't know why it has done this, but re-starting bqStudio has cleared the erroneous data in my experience.
In addition to Vish's suggestions which you have tried, confirm that your thermistors are attached. Residual voltages on TS1, TS2, or TS3 can prevent proper boot of the device. The bleed resistor on CAPn pins noted is a good troubleshooting technique but is not required in normal operation. The pull down of TSn to the appropriate reference is required for operation.
If I induce an XREADY on the middle group which is possible from a floating TS2 pin, my result is similar to yours. All bq76940 voltages report as 0, so the bq78350 applies the calibration values for the cells and the bqStudio display is some low value similar to your picture. The battery voltage is the sum of those voltages and is low. The temperature data is erroneous.
The bq78350 will attempt to clear XREADY, if it is successful the display should correct on an update. There may be parameter settings in the gauge which would let it create a PF or for you to read status with a command to observe the XREADY status.
When you disconnect cells bias is removed from the part and will allow nodes to discharge. The time to do the operation will also allow some discharge. You might try waiting a similar long time after shutdown before re-boot to see if it will wake properly. Check the connection at TS2 in particular, or its ability to measure temperature correctly when operating normally. If the part is connected correctly and the issue persists, the AFE may have been damaged during board processing.

Hi Alexander,
Odd, I see your Nov 6 reply noting finding the problem only after my post. Glad to hear you found the issue confirming my suspicion. Thanks for the suggestion on the data sheet.