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Puzzling behaviour od AD5336

		            
		

			

									
					    GordonS
					
							


			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 27, 2012 
				
			
			
		
    
		
     
				
		
    
		    		    
		    
		    	
			
    Hi Guys,
    
 
    I'm driving an AD5336 and my test code steps from 0 to 1023, then repeats until I stop it.
    
 
    The chip has a 3V3 supply and all of the Vref pins are at 3V0. LDAC and GAIN are both 0V and PD is at 3V3. Outputs are presently not disconnected to preclude any external influence.
    
 
    The puzzle is that, rather than rising 0V to 3V0 over the count as I expect, it ramps from 0V to 2V5 over the data range 0..~350, then stops rising.
    
 
    I can see all the data changing as I expect and even if I had bits swapped or stuck, I would not see the steady ramp to 2V5.
    
 
    I've replaced the chip, but still get the same behaviour.
    
 
    Can anyone shed any light on this, please?
    
 
    Thanks.
    
 
    Message was edited by: Gordon Scott (correction .. strikeout of inadvertant 'not')
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 AD5336
                
                                                    
                 Voltage Output D/A Converters
                
                                                    
                 Multichannel Voltage Output D/A Converters
                
                                
            
    
    
    

		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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                on Feb 29, 2012 11:11 AM
            
                                    
					
        
	
        

		
		
        
					
        Hi Padraic,
        
 
        I think the image isn't inverted, I'll explain more. If after that you still think it's inverted, then that is likely a clue.
        
 
        The upper image shows all output levels with the data stepping 0x200, 0x100, 0x080, 0x40, etc. So I would expect to see analogue levels of 1.5V, 0.75V, 0.375V and so on. Withe hindsight I should also have used 0x3FF to show fsd, but I was checking the individual data bits were working.That said, I'm confident it would just have widened the first level, not been any higher.
        
 
        There is nothing connected to the outputs. Sorry, in my original post I'm intended to change "not connected" to disconnected, and ended up with "not disconnected", which was incorrect. I corrected that a short while ago, but probably too late for you to notice the correction. They're disconnected partly because I suspected an external effect and partly because I had previously had a 100R/1nF lowpass, whcih caused the DAC to oscillate.  They are all now removed and, whilst I doubted the DAC was harmed I also replaced that. Old and new DAC both show the same behaviour.
        
 
        The pin I was looking at was p5 (VoutA), but all four do the same thing.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Feb 29, 2012 11:11 AM
            
                                    
					
          
	
          

		
		
          
					
          Hi Padraic,
          
 
          I think the image isn't inverted, I'll explain more. If after that you still think it's inverted, then that is likely a clue.
          
 
          The upper image shows all output levels with the data stepping 0x200, 0x100, 0x080, 0x40, etc. So I would expect to see analogue levels of 1.5V, 0.75V, 0.375V and so on. Withe hindsight I should also have used 0x3FF to show fsd, but I was checking the individual data bits were working.That said, I'm confident it would just have widened the first level, not been any higher.
          
 
          There is nothing connected to the outputs. Sorry, in my original post I'm intended to change "not connected" to disconnected, and ended up with "not disconnected", which was incorrect. I corrected that a short while ago, but probably too late for you to notice the correction. They're disconnected partly because I suspected an external effect and partly because I had previously had a 100R/1nF lowpass, whcih caused the DAC to oscillate.  They are all now removed and, whilst I doubted the DAC was harmed I also replaced that. Old and new DAC both show the same behaviour.
          
 
          The pin I was looking at was p5 (VoutA), but all four do the same thing.
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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