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ADuM3220 Production
The ADuM3220/ADuM32211 are isolated, 4 A dual-channel gate drivers based on the Analog Devices, Inc., iCoupler® technology. Combining high speed CMOS and...
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ADuM3220 on Analog.com

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Outputs 2 V while the supply is only 14V.

		
	
				

			

									
					    LarryADI
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 11, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
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                The user observed an output voltage higher than the supply voltage (17V vs 14V) when using ADuM3220 to drive MOSFETs as a solid-state relay. The support engineer suggested this could be due to inductive effects in the gate or hot loop, and recommended using a differential probe for measurements. Adding a 10uF capacitor across pins 5 and 8 improved the waveform, and the user is considering using ADuM3221 to drive multiple MOSFETs.
                        	    
    
                
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    Category: Hardware
    
    		        		            		    
    Product Number:  ADuM3220 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi tech support,
    

    I am using ADuM3220 as a floating gate driver to drive a pair of MOSFETs that had both source pins tied together, and both gate pins tied together, as a solid state relay. This configuration is used in order to keep the MOSFET body diode from conducting when Vgs is off.  Everything works fine except I noticed that the output (to gates of the MOSFET pair) swings from zero to 20 volts, while the isolated supply itself is only 14 volts.  why and how is the output boosted to 20V? I'm not aware of such boost descriptions in the datasheet. 
    

    The external floating supply + is connected to pin-8 and supply ground is connected to pin-5.
    

    

    

    Thanks for your help,
    

    Larry
    
			
    
			
									
		                             
                        

    
    
                                            
                 hardware
                
                                                    
                 Digital Isolation Technology
                
                                                    
                 Isolated Gate Drivers
                
                                                    
                 adum3220
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Sep 12, 2025 5:17 AM
            
            
						
			            		
      
		
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      Hi LarryADI, 

      Could you please share a scope capture of the waveform you are observing on the gate and a schematic snippet showing the MOSFETs and the ADuM3220 connections and the probing points? 

      Regards,
      Luca
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Sep 15, 2025 9:50 AM
            
            
												
						in reply to LMartini
					
										
			            		
        
		
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        Hi Luca, 
        

        Thanks for getting back to me. I have inserted the schematic and the scope waveform of the described problem. When I took the scope shot, the output (yellow line) at the ADuM3220 actually peaked at about 17V instead of 20V, while the isolated power supply input is only 14V. What's baffling me is how I can get an output higher than the supply voltage. And also notice that the output level is not uniform, it first climbed up to 10V then ramps its way up to 17V.  Does it have to do with the fact that there's a monolithic transformer (and therefore an inductor) inside the ADmU3220?   
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
						
                            
            
            				
            
                on Sep 18, 2025 6:37 AM
            
            
												
						in reply to LarryADI
					
										
			            		
        
		
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        Hi LarryADI, 
        

        I suspect this apparent voltage "bumb" is caused by some inductive effect in the hot-loop or in the gate-loop.
        A couple of questions:
        

        1) Do you see this same effect on Vgs when the power MOSFETS are not energized, and so there is no current flowing through drain-source of the power devices?
        

        2) Are you using a differential probe to measure the Vgs? by using a differential probe, can you take a scope capture between pin 5 and pin 7 of ADuM3220 and repeat the same measurement at the gate/source pins of the power MOSFETs?

        Regards,
        Luca
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
						
				
				
		
		
        
			
		
        
	
        

        

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                on Sep 18, 2025 7:04 PM
            
            
												
						in reply to LMartini
					
										
			            		
          
		
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          Hi Luca,
          

          Unfortunately it's difficult for me to observe it with no load through MOSFETs.  The output of the ADuM3220 without driving MOSFETs looks ok.     I had a 1uF capacitor across pins 5 and 8 and observed that "bumb",  I added an additional 10uF electrolytic cap and saw an improved waveform. 
          

          By the way I am using one output channel of ADuM3220 to drive the Vgs of 6 MOSFETs. Could it be part of the problem? 
          

          Should I try ADuM3221 and tie both inputs and outputs together for driving 6 MOSFETs?
          

          Attached is a picture of the improved waveform at Vgs after I added the 10uF cap across pin 5 and 8. 
          

          Please comment.  Thanks,
          

          Larry 
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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