LTC6813 communication issue - Linduino DC2792B

if you don't know the isoSPI polarity or ISOMD configuration on the LTC6813 this may be hard.  The easiest thing to do is flip the isoSPI cable wires as there will be no response if they are reversed.  Are there any differences to the power section of the IC from DC2350B?  Although it's certainly unusual to use only 6 cells with LTC6813 as long as 16V is present at V+ it should not be a problem.

Hi

Thanks for the reply. I initially made a mistake, the 6813 is setup to measure 12 cells in series. I have measured and there is 44V on V+. The linduino is powered over my USB connection while the 6813 is powered directly off of the cells.

I also tried flipping the IC wires and didnt get a response in either setup.

ISOMD is tied to VReg on 6813.

I have measured Rb1 and Rb2 on the DC2350B and also on the LTC6813 PCB and found they are different - I was thinking maybe the difference in resistors would affect the differential pulse that is detected by the 6813. The DC2350B has 1k resistors for both, whereas the 6813 has 2.8k for R1 and 1.2k for R2 (this matches exactly the figures in the datasheet).

Additionally there are no termination resistors (RM), but I have measured setup in the vehicle and there are no termination resistors either. Both use 1:1 transformers.

Appreciate this info may not be relevant, just setting up what I have.   

b8trez said:

I was thinking maybe the difference in resistors would affect the differential pulse that is detected by the 6813. The DC2350B has 1k resistors for both, whereas the 6813 has 2.8k for R1 and 1.2k for R2 (this matches exactly the figures in the datasheet).

This is possible.  The 6813 is set to substantially lower current in this configuration.  We recommend R1=1.4kohm and R2=604ohm for optimal performance (or closest standard value resistor you have) and to use the same configuration for both the cell monitor and tranceiver.

b8trez said:

Additionally there are no termination resistors (RM), but I have measured setup in the vehicle and there are no termination resistors either

isoSPI requires termination resistors as it is a current controlled signal.  Is the part LTC6813-1 or LTC6813-2?  If LTC6813-2 then termination resistor only goes at the end of the multi-drop.

Just to round out the question - I applied the R1 and R2 mentioned above now have comms with the LTC chip