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ADUM1401 Production
The ADuM1400/ADuM1401/ADuM1402 are quad-channel digital isolators based on Analog Devices, Inc., iCoupler® technology. Combining high speed CMOS and monolithic...
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ADUM1401 on Analog.com

ADUM5402 Production
The ADuM5401 / ADuM5402 / ADuM5403 / ADuM5404 are quad-channel digital isolators with isoPower®, an integrated, isolated dc-to-dc converter. Based on...
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ADUM5402 on Analog.com

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ADUM1401, ADUM5402, SPI, "three state"

		
	
				

			

									
					    Tommaso
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Feb 29, 2012 
				
			
			
		

		
		                     
				
        		

		    
		    		    
		    			

			    
Hello,

 
I would like to ask the following question about ADUM1401C and ADUM5402C.

 
I would use ADUM1401C and ADUM5402C to interface to an SPI bus a section of a circuit which has to be isolated. On the SPI bus are connected also other two devices.

 
So, how is it possible to get in "three state" the outputs of ADUM so that other devices can transmit over the bus without collisions?

 
I thought to obtain the objective by powering off ADUM's SPI side when other devices have to use the bus, but I'm not sure it could be a good solution since AN-825 consider this power state as "special condition" and the time between the supply is on and the ADUM can work as specified con be an issue. (Is this time known?)

 
Thanks a lot for the help.

 
Regards,

 
Tommaso

			

			
									
		                             
                        

    

                                            
                 isopower
                
                                                    
                 Digital Isolation Technology
                
                                                    
                 adum5402
                
                                                    
                 adum1401
                
                                                    
                 Standard Digital Isolators
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Feb 29, 2012 2:13 PM
            
            
						
			            		
    
		
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    Hello Tommaso,
    
 
    It sounds like you will be having the traffic from the isolated SPI device sharing a common bus with other SPI devices so that only one SPI device at a time will be enabled to have control of the MISO line.  In your case it should be straight forward.  Use the ADuM1401 "D" channel for the MISO line.  There is a enable pin that will tristate all of the outputs on side 1.  Since there is only one output, it simpley becomes an output enable for that pin.  Use the chip select line for the isolated device to control VE1.  You might need an inverter to correct the logic.
    
 
    MSCantrell
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    

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