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Standard digital isolator for I2S audio line



		

			

									
					    usaghi
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 18, 2014 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    
 
    We are now studying to use ADI standard digital isolators for I2S, not I2C-bus but Inter-IC sound bus, replacing for legacy photo couplers. 
    
 
    One considering I have is I2S is seemed to be specified as TTL type of logic which VIL=0.8V and VIH=2.0V, subject to I2S bus specification of Feb.1986 (but it notes: <At present, TTL is considered a standard for logic levels. As other IC (LSI) technologies become popular, other levels will also be supported>, however I can not find out any newer specifications, so far), against ADI isolator seems to be using CMOS logic level.
    
 
    Could you please make sure whether ADI's standard digital isolators are suitable for insulation in I2S digital audio lines ?
    
 
    Or, if you provide any note of caution when using isolators in I2S lines, it would be very much appreciated.
    
 
    I may add that devices of our interest are, for example,  ADuM751x, ADuM348x, ADuM228x, ADuM128x or others.  
    
 
    Best Regards,
    
									
			        
		
    

				
						
        

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 31, 2014 4:10 PM
            
            
					
      
	
      

		
		
      
					
      Hello Takehisa
      
 
      Our isolators are al built on CMOS processes, it is a choice at design time if we adjust the switch point to be for TTL input ot CMOS input levels.
      
 
      Whether to add translation buffers or not depends on what you have on the bus.  Our parts with CMOS outputs will be compatible with the TTL inputs, but other devices talking on the bus may or may not be able to supply a VOH high enough to guarantee that we can read it as a high level.  If you have components that can not drive the line to 0.7xVdd, then you may need a level shifter.  I would review the other components output specs in detail if you want to use a component like the ADuM7510.
      
 
      If CL is larger than speced, you can get a good idea how the output will respond by knowing that the channel impedance of our outputs is about 70ohms, you can make that part of an RC network that pulls the line up or down.  It is a bit crude, but it will tell you if you need to worry.
      
 
      Level shifting will have some propagation delay I am sure, so it needs to be examined.
      
 
      I hope this helps.
      
 
      Best Regards,
      
 
      MSCantrell
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 31, 2014 4:10 PM
            
            
					
      
	
      

		
		
      
					
      Hello Takehisa
      
 
      Our isolators are al built on CMOS processes, it is a choice at design time if we adjust the switch point to be for TTL input ot CMOS input levels.
      
 
      Whether to add translation buffers or not depends on what you have on the bus.  Our parts with CMOS outputs will be compatible with the TTL inputs, but other devices talking on the bus may or may not be able to supply a VOH high enough to guarantee that we can read it as a high level.  If you have components that can not drive the line to 0.7xVdd, then you may need a level shifter.  I would review the other components output specs in detail if you want to use a component like the ADuM7510.
      
 
      If CL is larger than speced, you can get a good idea how the output will respond by knowing that the channel impedance of our outputs is about 70ohms, you can make that part of an RC network that pulls the line up or down.  It is a bit crude, but it will tell you if you need to worry.
      
 
      Level shifting will have some propagation delay I am sure, so it needs to be examined.
      
 
      I hope this helps.
      
 
      Best Regards,
      
 
      MSCantrell
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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