LTC6813 communication issue - Linduino DC2792B

Question

Hi 
 I am working on a project trying to communicate with a LTC6813 setup measuring 6 cells in series. I have a linduino and DC2792B to communicate via isoSPI.I am also using the arduino libraries provided by analogue devices inc. Unfortunately I am not getting communications with the LTC6813. 
 The battery comes from a vehicle that is made up of multiple modules. They use isoSPI to communicate as the BMS has 6820 deployed. I am trying to communicate with the final module which has a 2 wire comms connection. 
 Are there any debugs I could try to try and get comms. I have checked pins and scoped the isoSPI line and all seems correct. 
 Many thanks 
 Jack

mvrablic · Accepted Answer

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.)

mvrablic · Answer

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.

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LTC6813 communication issue - Linduino DC2792B

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