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Class AB & HPOUT DC bias



		

			

									
					    MasterAudio
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 13, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    		            		        
    Category: Hardware
    
    		        		        		    		    	
			
    Hi ADI,
    

    I have some confuse, as I know the class AB output dc bias approach to zero
    

    Why HPOUT+ and HPOUT- have a half dc voltage of VDDHP
    
									
			        
		
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      •  Super User  
      
            
			                            
                        
                on Sep 13, 2022 10:28 PM
            
            
					
      
	
      

		
		
      
					
      Hello MasterAudio,
      

      Because the output circuits are class AB and will sit at AVDD/2 and it is not possible to put a large cap on the silicon die so it has to be done externally. The enables the output to swing positive and negative with respect to the CM ( common Mode) voltage level. These parts do not have a positive and negative power supply rails, only single ended power so therefore "0" signal level has to be midway of the power supply. 
      

      You can use the CM pin as a reference for an OpAmp circuit to amplify it without caps or the easiest and best way is to place a series cap to block the DC and allow for a simpler design of output amplifier. 
      

      In the case of headphones, it does not matter if it does not touch ground. It is still a good idea to use caps if it fits into your design budget. 
      

      Did I answer your question? Please feel free to share why this is a problem for you?
      

      Dave T
      

      BTW, Let me know which part you are looking at. 
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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