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ADUM1411 Production
The ADuM1410/ADuM1411/ADuM1412 are four-channel digital isolators based on Analog Devices, Inc. iCoupler® technology. Combining high speed CMOS and monolithic...
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ADUM1411 on Analog.com

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ADUM1411 with unpowered VDD1

		
	
				

			

									
					    Detlef
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Aug 4, 2021 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Hello,
    

    I'm using 12pcs. ADuM1411 in oder to drive isolated ADCs with a single SPI. In my design I connected MISO to V_OD of all ADuMs.
    

    The Idea was to use a transistor to power up VDD1 only when needed (i.e. when CS goes low).
    

    Looking at the truth table in the datasheet, V_OD should go High-Z when VDD1 is unpowered and the output pins V_OA, V_OB and V_OC should go high (assuming CTRL1 is unconnected).
    

    But this is not the case. Even with VDD1 completely disconnected the ADuM is still passing signals from V_IA to V_OA and VDD1 is **sourcing** 2.4V!! Only when I tie VDD1 to GND1 I can see the specified behavior (but then I have 50mA(!) running from VDD1 to GND1).
    Is there anything I'm missing here?
    

    Thanks in advance!
    

    Detlef
    
			
    
			
									
		                             
                        

    
    
                                            
                 Digital Isolation Technology
                
                                                    
                 adum1411
                
                                                    
                 Standard Digital Isolators
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Aug 4, 2021 12:22 PM
            
            
						
			            		
      
		
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      Hi Detlef,
      

      VOD should go High-Z when Vdd2 is powered and Vdd1 is unpowered. That means VOA , VOB and VOC will have their input side (Vdd1) unpowered, and output side (vdd2) powered so these outputs will be in the default state, determined by the CTRL2 (Not CTRL 1). If CTRL2 is unconnected or high then VOA VOB and VOC will go high. CTRL1 controls VOD not VOA VOB AND VOC.
      

      Regards,
      

      Naveen
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Aug 4, 2021 12:22 PM
            
            
						
			            		
      
		
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      Hi Detlef,
      

      VOD should go High-Z when Vdd2 is powered and Vdd1 is unpowered. That means VOA , VOB and VOC will have their input side (Vdd1) unpowered, and output side (vdd2) powered so these outputs will be in the default state, determined by the CTRL2 (Not CTRL 1). If CTRL2 is unconnected or high then VOA VOB and VOC will go high. CTRL1 controls VOD not VOA VOB AND VOC.
      

      Regards,
      

      Naveen
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Aug 5, 2021 3:05 AM
            
            
												
						in reply to Naveen Afzal
					
										
			            		
        
		
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        Thanks for your quick response.
        

        But VOD doesn't go High-Z when Vdd2 is powered and Vdd1 is unpowered as long as VIA, VIB or VIC are still receiving signals. I'm using VIA and VIB for CLK and MOSI in parallel to all ADUMs
        

         
        

        Pin1 is not connected. If pulled to GND VOD goes high-Z, but I see 50mA running from pin1 to gnd.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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