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LTC6813 responding with 0xFF for everything



		

			

									
					    sindagi2
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 30, 2018 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    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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      •  Analog Employees  
      
            
			                            
                        
                on Dec 13, 2018 2:39 PM
            
            
												
						in reply to sindagi2
					
									
      
	
      

		
		
      
					
      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
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
        
            
			                            
                        
                on Dec 17, 2018 10:39 AM
            
            
												
						in reply to ADIApproved
					
									
        
	
        

		
		
        
					
        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
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
        •  Analog Employees  
        
            
			                            
                        
                on Jan 17, 2019 2:18 PM
            
            
												
						in reply to sindagi2
					
									
        
	
        

		
		
        
					
        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
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Feb 11, 2019 9:59 AM
            
            
												
						in reply to Harshit.Analog
					
									
          
	
          

		
		
          
					
          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
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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