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AD9280 Production
The AD9280 is a monolithic, single supply, 8-bit, 32 MSPS analog-to-digital converter with an on-chip sample-and-hold amplifier and voltage reference....
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AD9280 on Analog.com

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AD9280 - 1V input at AIN pin with 0.5V offset

		
	
				

			

									
					    MP778
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 12, 2020 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Hi,
    

    I have 1V input (0.5 offset) connected to AIN pin of the AD9280. The AD9280 is connected as per Figure 18 (Internal Reference - 1 V p-p Input span Top/Bottom mode).
    

    Once I apply the 5V at AVDD and DRVDD, output D7 is stuck at high for about 80 seconds before it starts giving some sensible reading.
    

    different signal on the ADC pin reads as below:
    

    AVDD, DRVDD, MODE - 5V
    

    Clock - works as expected at power up
    

    VREF, REFSENSE, REFTS - 1V
    

    REFTF wrt REFBF -1V.
    

    REFTF wrt 0V = 3V
    

    REFBF wrt 0V = 2V
    

    D7 - 5V
    

    D6 - 0V
    

    D5 - 5V
    

    D4 - 5V
    

    this data line suggests the input is very high which is not. OTR line stays low all the time. TRI and STB lines are always low.
    

    Why I am seeing data out stuck at this level for about sometime before it settles?
    

    Have I got correct mode for the input type?? Please reply as soon as possible. Thanks,,
    
			
    
			
									
		                             
                        

    
    
                                            
                 ad9280
                
                                                    
                 High Speed A/D Converters >10 MSPS
                
                                                    
                 Standard High Speed A/D Converters
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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							FormerMember
					
      
		
      
		    
		    		    
			
				
									FormerMember
							        
			
			
			
    
            
						
                            
            
            				
            
                on Feb 12, 2020 11:34 AM
            
            
						
			            		
    
		
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    Hello,

    Voltages appearing at non-digital output pins appear correct.

    Input span should be 0 to 1 V at the AIN pin thus voltage inputs from approximately 0 to 1 V should provide digital codes of 0x00 to 0xFF.
    One can monitor the OTR to determine the  -FS voltage and +FS voltage (referring to figure 32).  When OTR is reached at low end of -FS (around 0 V).............digital code should read 0x00 and on high end of +FS (approximately 1 V) it should read 0xFF.  Once your determine these voltage inputs.......you can then change voltage input level to fall within -FS and +FS and read codes that fall between these lower and upper limits.
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    


	

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							FormerMember
					
    
		
    
		    
		    		    
			
				
									FormerMember
							        
			
			
			
            
						
                            
            
            				
            
                on Feb 12, 2020 11:35 AM
            
            
						
			            		
    
		
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    Note.......comments above assume a DC input from a low source impedance input (op amp, ext).
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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                on Feb 13, 2020 6:12 AM
            
            
												
						in reply to FormerMember
					
										
			            		
      
		
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      Thanks for the reply. at no inputs the digital output should be low. Should I be doing anything to the CLAMP signal? Thanks
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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