LTC6813 responding with 0xFF for everything

Hi Chai, 

As per the data provided , we see that ADC conversion is not happening as Vref1 & Vref 2 are 0V, They should be in the range as mentioned in the datasheet page no:5.

If you can share your schematic we can try to understand the issue.

I also found this elsewhere on the forum where someone is having the same issue on the LTC6804 and LTC6811 parts

ez.analog.com/.../ltc6804-2-and-ltc6811-2-reference-voltage-1-and-2-at-0v

Hi, 

1. VREF1 can be observed when ADC Conversion is happening. It can be measured using DSO.

2. From the Schematics i cannot see a pull up resistor on SDO( MISO) line. So if there is no pull up then communication will not happen.

Please confirm for the above 2 points.

Phani

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,

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