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LTC6813 responding with 0xFF for everything

I'm using the LTC6813 on a custom built PCB, and have the reference Linduino software that I got from here running on an Arduino Uno.

The VREG bus is at 5.25V and then turns off after 2s if no command is received(as expected), however, the VREF1 and VREF2 pins are at 0V.

When the evaluation software requests information from the device of any sort, the SDO is held high (0xFF) during the data part of the transmission, but a PEC of 0x66, 0x4C is transmitted as well. 

When I send the command "1" to the Linduino software (Write and Read Configuration: 1), I get this as the output - 

Written Configuration:
CFGA IC 1, 0xE4, 0x0D, 0x28, 0xA0, 0x01, 0x00, Calculated PEC: 0xAD, 0x6A
CFGB IC 1, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, Calculated PEC: 0xC2, 0x12

Received Configuration
CFGA IC 1, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, Received PEC: 0x66, 0x4C
CFGB IC 1, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, Received PEC: 0x66, 0x4C

Reading cell voltages in a loop (command 11) gives me -

Cells, 6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,

I am unsure what is going on since obviously the chip is responding to commands with messages that have a valid PEC value. 

Thanks in advance, I'm happy to provide any more information that you'd like, including schematics of the board to find any hardware issues, if there are any. 

Chai

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  • Hi,

    1. I am unsure what a DSO is. I was measuring the voltage across the filter cap with an oscilloscope and could not see any voltage.

    2. The communication is working correctly, I am receiving a valid PEC. However, the data frame is just repeated 0xFF. The pull up is enabled internally on the microcontroller.

    UPDATE: We have working communications occasionally with no obvious change in configuration

    Chai

  • Hi Chai,

    Please find the latest sketch book code for LTC6813. Try using this code.

    I hope, this should resolve your problem. 

    6813_SKETCHBOOK_Code.zip

  • I used the code in the sketchbook above and this did not rectify the issue. 

    However, I believe I have identified the issue with the board, but am completely lost for a solution. I used a redesigned board with some minor hardware changes including an LED that indicated power status as well as one to indicate the WDT status. These two resulted in my observation below. 

    When the LTC6813 sketchbook is on command 10 or 11(pull voltage data in a loop), the power LED turns on when VREG goes to 5.3V and stays there for 2 seconds. The small dip in voltage I was observing before at the end of 2 seconds was now a drop to 1.4V, approximately the forward voltage of the indicator LED, likely due to the much higher current draw from LED compared to only the LTC6813 before. Moreover, the WDT pin goes into high impedance and the LED connected to it briefly turns on as well. This would indicate that the WDT expires and the chip enters STANDBY, but right after it does so, a communication signal from the sketchbook code causes it to turn on again. 

    I can only attribute this to the chip perhaps not recognizing the command from the sketchbook, and thus, deeming it an invalid message, allows the WDT to expire. I am not sure why this is happening or how I may rectify the issue, but I have not been able to communicate with any of the 5 LTC6813 chips I have bought so far and am starting to believe that perhaps I received a faulty early batch and am suffering the consequences. Will I have to buy a new batch of chips to test or is there perhaps some bug in the sketchbook itself or the setup of the code before compiling it that I have missed?

    Hoping I receive a quick reply since time is running out for me on this project and I must move on to further testing ASAP

    Thanks and Regards

    Chai