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ADuM12980:  Is this isolator capable of driving a TTL load on the output side and accepting a CMOS on the input?



		

			

									
					    williajl43
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Apr 13, 2017 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I have been forced to find some type of replacement for a Toshiba TLP2105(F) optocoupler, due to availability issues lately.  I have been looking into the iCoupler family, but the documentation makes it difficult to see if there is a suitable replacement.  What I am looking for is a two channel unidirection isolator that accepts CMOS 3.3V logic on the input side and can drive TTL 5.0V on the output side.  What is not clear is the drive current capability of these chips on the output channels.  Can I use the ADuM12980 for this purpose?  What options do I have for this?  Is there any special PCB layout that I need to follow? Can I use this or any of the iCoupler in a tight board layout design?  I need some guidance on this since I am new to this approach. The actual speed of my signaling for the inputs will be from DC to 5KHz max.
    
 
    Thanks
    
 
    James
    
									
			        
		
    

				
						
        

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi James,
      
 
      Welcome to the world of digital isolation. I think you'll like it here! 
      
 
      Its no problem having 3.3V CMOS inputs and driving 5.0V TTL loads. The layout is simple. You just pick your favorite 2-channel device and two good 0.1uF bypass caps. One bypass cap on the VDD1 side. One bypass cap on the VDD2 side. Keep the caps close to the pins so they can do their job. That's it for the layout.
      
 
      The input and output voltage levels will scale with the VDDx pin on the same side of the device. It sounds like you need a 3.3V supply on the VDD1 and 5.0V supply on VDD2.  
      
 
      The drive strengths are given in DC Specifications Table. Refer to Logic High/Low Output Voltages and the test conditions. You will find the standard data isolators can drive 2 TTL loads. 
      
 
      We have a handful of different 2-channel devices that will do just what your asking for. The first decision to narrow the field is figuring which output default is appropriate for your design. When the input VDDx is not powered and the output VDDx is, the output will either drive high or drive low. That is your output default. It is difference between the ADuM1280 and ADuM1285 for example. 
      
 
      You can look at ADuM3210, ADuM1280, or ADuM120N for your application. All of these parts will do DC to 5kHz and beyond. Let me know if I can help explain or narrow down the choices further.
      
 
      Regards,
      
 
      Jason
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi James,
      
 
      Welcome to the world of digital isolation. I think you'll like it here! 
      
 
      Its no problem having 3.3V CMOS inputs and driving 5.0V TTL loads. The layout is simple. You just pick your favorite 2-channel device and two good 0.1uF bypass caps. One bypass cap on the VDD1 side. One bypass cap on the VDD2 side. Keep the caps close to the pins so they can do their job. That's it for the layout.
      
 
      The input and output voltage levels will scale with the VDDx pin on the same side of the device. It sounds like you need a 3.3V supply on the VDD1 and 5.0V supply on VDD2.  
      
 
      The drive strengths are given in DC Specifications Table. Refer to Logic High/Low Output Voltages and the test conditions. You will find the standard data isolators can drive 2 TTL loads. 
      
 
      We have a handful of different 2-channel devices that will do just what your asking for. The first decision to narrow the field is figuring which output default is appropriate for your design. When the input VDDx is not powered and the output VDDx is, the output will either drive high or drive low. That is your output default. It is difference between the ADuM1280 and ADuM1285 for example. 
      
 
      You can look at ADuM3210, ADuM1280, or ADuM120N for your application. All of these parts will do DC to 5kHz and beyond. Let me know if I can help explain or narrow down the choices further.
      
 
      Regards,
      
 
      Jason
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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