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Products Mentioned

ADM2861E Recommended for New Designs
The ADM2861E, ADM2863E, ADM2865E, and ADM2867E are 5.7 kV rms signal and power isolated RS-485 transceivers. These devices are designed for balanced transmission...
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ADM2861E on Analog.com

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No  RxD data at low temperature

		
	
				

			

									
					    Kobr
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Mar 12, 2024 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user experienced no received data at the RxD output of an ADM2861E RS-485 transceiver at -15°C, with the RxD pin voltage dropping to 2.2V. The issue was resolved by moving decoupling capacitors C11 and C14 closer to pins 4 and 7 on the same layer, reducing loop impedance. The final answer confirms this solution and suggests closing the thread.
                        	    

                
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Category: Hardware

    		        		            		    
Product Number:  ADM2861E  

    		        		    		    

		    		    
		    			

			    
Hi, I am using an ADM 2861 E transceiver in my device to communicate via RS 485. This device must work in the operating temperature range from -30°C to +60°C. At standard room temperature, the transceiver operates normally, Vcc, Vio = 3.3 V.


 


 


In a climatic chamber at a temperature of -15 °C, the device is switched off and after switching on, no received data at the RxD output, and the voltage on this pin is 2.2 V.


  


If I briefly heat up, for example, pin 14 GND1, the data appears.

			

			
									
		                             
                        

    

                                            
                 hardware
                
                                                    
                 Digital Isolation Technology
                
                                                    
                 adm2861e
                
                                                    
                 Isolated RS-485
                
                                                    
                 interface
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Mar 13, 2024 6:26 AM
            
            
						
			            		
    
		
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    Hi,
    

    In order to better understand the situation, I would have a few questions.
    

    Firstly, could you share the layout of the board and the test setup?
    

    In particular, does the communication data come to the device directly from pins A and B or from the TxD pin (and then read by the receiver)?
    

    Would it be possible for you to replicate the test by also showing this data (TxD, A, B)?
    

    In the meantime, could you measure the supply voltages (VDD and VISOin)?
    

    While we wait for your feedback, I will continue to analyze the issue.
    

    Thank you,
    

    Andrea
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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                on Mar 19, 2024 7:13 AM
            
            
												
						in reply to AndreaRusso
					
										
			            		
    
		
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    Hi Andrea,  
    

    

    thank you for your answer which helped me.
    

    I tested the transceiver with a feedback loop TxD input RxD output.
    

    The cause of said problem was a bit long path and two vias between pins 4 and 7 and capacitors C11 and 14. When I moved these capacitors as close as possible to pins 4 and 7 on the same layer as the AMD 2861E the problem was solved.
    

    

    

    

    

    

    

     
    

    

    Thank you, 
    

    

    Martin  
    

    

    

    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Mar 20, 2024 1:16 PM
            
            
												
						in reply to Kobr
					
										
			            		
    
		
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    Hi Martin!
    

    I'm happy to hear that you solved the problem. I agree with your solution. In general, where possible, it is good practice to minimize the loop impedance of the decouping capacitors as seen from the power pins.
    

    Since the problem has been resolved, I will close the thread. If any other problems or concerns arise, please do not hesitate to open another request.
    

    Good work!
    

    Andrea
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    

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