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AD7124-8 Recommended for New Designs
The AD7124-8 is a low power, low noise, completely integrated analog front end for high precision measurement applications. The AD7124-8 W grade is AEC...
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AD7124-8 on Analog.com

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AD7124-8 Internal temperature sensor conversion cause AINM_UV_ERR



		

			

									
					    KennethPD
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 9, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hello :) 
    

    We're implementing an AD7124-8 as the main ADC in test equipment and I am in the process of writing up the firmware for controlling the module where the ADC is placed. I would like to measure the die temperature of the ADC to perform auto-calibration when large temperature changes happen. 
    

    I had gotten what seemed to be believable temperature conversions from the built in temperature sensor, but then I enabled error handling for the conversions, thereby including the conversions made for the internal temperature sensor, and now I get AINM_UV_ERR for every conversion with the internal temperature sensor. 
    

    I have following configuration for the channel (Channel 7) that converts the internal temperature sensor: 
    

    - AINP = 16/Temperature sensor
    

    - AINM = 17/AVss
    

    - Setup = 4
    

    The configuration and filters are set as follows (for setup 4)
    

    - Internal reference 
    

    - Bipolar 
    

    - 1 x Gain 
    

    - FS = 32 
    

    The conversion is done by enabling the channel and doing a single conversion in full power mode. Reading the error register following that, reveals that AINM_UV_ERR gets set. 
    

    As I said, the resulting temperature (if you ignore the error and read the conversion result) seems reasonable, so is this just expected behaviour? Can I believe the results I am getting, and just ignore the undervoltage error? 
    

    br. 
    

    Kenneth
    

    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			








	
	
	
	



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                on Nov 15, 2021 1:57 PM
            
            
												
						in reply to andreialejandro
					
									
        
	
        

		
		
        
					
        Hello 
        

        Maybe I should have explained it a bit clearer, but its not using Pin 17. It is muxed via the internal mux to AVSS aka. 17 (Decimal) in the AINM field of the channel register. This means that the converter is connected to the internal temperature sensor, with AINP to the temperature sensor (16 decimal in the AINP field), and AINM is connected to AVSS (17 decimal in the AINM field). I hope this clears things up how the internal mux is configured. 
        

        /Kenneth
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        •  Super User  
        
            
			                            
                        
                on Nov 15, 2021 2:34 PM
            
            
												
						in reply to KennethPD
					
									
        
	
        

		
		
        
					
        Hi,
        

        Apologies for confusion. We have tested and guaranteed that every part will trip at 40mV outside the rails as shown in the figure in the datasheet. However, you will see that other parts may also trip at different voltages near the rails and this varies from part to part, that is why we do not have a specs for this listed on the datasheet. The diagnostics uses a comparator and this not very precise and could have some offset errors. Some parts may trip at the rails and some are above or below the rails. So the flags can trip anywhere from the rails (AVSS/AVDD) to 40mV outside the rails. And like I said, the overvoltage/undervoltage checks are done using comparators so the checks occur on the analog input being measured and not upon conversion. The check is also continuously performed. So if you are using AVDD/AVSS as your input and the UV/OV error is enabled, the flag could be possibly set. 

        And this is the case on using internal temperature sensor as it works in conjunction with AVSS. 
        

        May I know how important the UV/OV errors in your system?
        

        Thanks,
        

        Jellenie
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
						
				
				
		
		
        
			
		
        
	
        

        

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                on Nov 15, 2021 2:58 PM
            
            
												
						in reply to JellenieR
					
									
          
	
          

		
		
          
					
          Okay, that would explain it! Loose detection of UV/OV, which I did notice in the datasheet to be a seperate circuit in the IC, just like you said, a seperate set of comparators. Tripping these errors doesnt necessarily mean that the converter itself is outside of the valid region, it is just the error detection that is too inaccurate to detect it. So just like I suspected in my first post, the converter result is valid, I will just have to ignore the UV/OV errors when performing temperature readings. 
          

          In the rest of my system I am not measuring near the rails, so in any other case than the temperature conversion I should still be able to use the UV/OV detection (While it might limit my range a bit if they have inaccurate tolerances) But the most important thing is that I know I get valid conversions, which these error checks should guarantee. 
          

          I consider my question answered! Thank you for your help 
          

          /Kenneth
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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