BQ35100: Issue communication with BQ35100

Hi,

Thank you for your quick reply!

Voltage at REG25 is 2.62V.  VBAT voltage is 3.75.  GE is 3.75 and REGIN is 3.75.

The device is brand new.  Working on bringing up a new board that was just built.  Do devices comes sealed or are they unsealed until they are sealed via commands?  No commands have been issued to the device.  Starting with a 1-byte read from register 0x0A.

Yes, following the I2C format from 14.1, specifically trying the 1-byte read.  The formatting appears correct as the start bit is issued and the first 7 bits get clocked it the ACK just doesn't happen.  See the scope shot for this confirmation.

I do not have an EV2400.

Any additional pins to check or other commands to run/send?

Thanks,

Mike

Hi Mike,

No immediate concerns with the LSF0204 schematic, though please ensure that the LS_EN pin follows similar to below:

Regards,

Jack

Yes, confirmed this is followed.  Any additional troubleshooting ideas to try?

Hi Diego, thanks I read through and verified this is being followed.

Upon examining the I2C communication, I noticed the SCL rise time is quite slow. The BQ35100 datasheet specifies a maximum rise time of 300 ns. I suspect the LSF0204RUTR level shifter’s bus capacitance is causing this issue. I tried reducing the pull-up resistor to 2.15 kΩ to improve the rise time  which got it down to 1.2uS (see image below), however, this is still far more than the maximum 300nS.  I tried lowering the pull up resistor further, however, this caused excessive current sink at the pins, disrupting I2C operation. Any suggestions to address this? I believe this slow rise time is the root cause of the problem.

Hi Jack,

I was taking an incorrect measurement.  Setting the scope probe to 10X, the rise time before and after the level shifter is less than 300nS so this does not appear to be an issue.  See image below 

I am still unable to communicate with the BQ35100.  Attached is the scope shot of the SCL and SDA lines.  It appears everything is clocking in properly but it isn't acknowledged by the BQ35100.  The 8-bit address of 0xAA is being sent as seen in this scope shot but there is no acknowledge.  

Is there anything initial sequence or unlock command that needs to be issued to the device first?  These are brand new parts.  I greatly appreciate any other items you can suggest to try.

Hello Mike,

Can you try addresses the gauge with the address of 0x16. It is possible that the gauge is in ROM mode which will only communicate to address 0x16.

Regards,

Adrian

Hi Adrian,

I did try with the address of 0x16 and it still did not acknowledge.  Any additional suggestions? 

Does the supply and/or voltage at REGIN need to be different than the BAT pin?

Yes, I removed the level shifter and have the SDA/SCL lines connected directly to the processor with external pull ups.  Still not able to get an ACK.

The TS lines starts high on startup and remains high for 510mS, goes low for ~120mS, then remains high and does not pulse again.  The voltage on the TS pin is 2.62V.