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AD8392A Production
The AD8392A is comprised of four high output current, low power consumption, operational amplifiers. It is particularly well suited for the CO driver interface...
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AD8392A on Analog.com

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Is pin 4 and pin20 connected internally for AD8392AACP(LFCSP package)?

		
	
				

			

									
					    howardaaa
					
							

            
            			
				
									
											
			
			
				
  •  Analog Employees  

			
			
			    	
			                    
                
				                on Jul 22, 2025 
				
			
			
		

		
		                     
				
        		

		    
		    		    

		      		            		        
Category: Hardware

    		        		            		    
Product Number:  AD8392A  

    		        		    		    

		    		    
		    			

			    
Hi, 


my customer is using AD8392AACP and the schematic is as below.


 


We are supplying PIN20 with 22V, but 18.4V could be found on PIN4(which is floating). Is PIN20 and PIN4 connected internally?


And for channel 2 OPA.


We measured VOUT2(PIN22)=18.4V, +VIN2(PIN25)=0V, -VIN2(PIN23)=3.0V, when R2073 resistor is unsoldered.


The circuit is equivalent to the case below:


RN=49.9ohm, VIN=0V, Rg=499ohm, Rf=2kohm,


we suppose the output to be 0V, but it's not.


 


What could be wrong with our circuit?


 

			

			
									
		                                 
Thread Notes  

                

        
                                        
                        

    

                                            
                 Operational Amplifiers (Op Amps)
                
                                                    
                 hardware
                
                                                    
                 AD8392A
                
                                                    
                 High Output Current Op Amps = 100mA
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

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    •  Analog Employees  
    •  Super User  
    
            
						
                            
            
            				
            
                on Jul 24, 2025 9:50 PM
            
            
						
			            		
    
		
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    Hi,
    

    

    Good day. As a rule of thumb, all supply pins should now be left floating. It must be connected to the appropriate supply voltage. There must be some internal coupling between pin 4 and pin 20, which is the reason why you measured a voltage on pin 4. Floating the supply pin could cause unstable/unpredictable operating for the part, which could damage the AD8392A. I would recommend checking the supply voltage level first before applying the input signal. Thanks.
    

    

    Regards,
    Gilbeys
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Jul 25, 2025 2:16 AM
            
            
												
						in reply to GLADION
					
										
			            		
    
		
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    Gilbeys,
    

    I've tried to power both PIN4 and PIN20 with 20V, and different voltages are observed with different resistor value for R2160 between PIN25 and GND.
    

    When PIN25 is floating(which represents R2160=Infinite), PIN25=0V, PIN23=3.9V, Vout=18.4V.
    

    When R2160=50ohm(IN+ connected to GND through 50ohm), PIN25=0V, PIN23=0.2V, Vout=1V.
    

    When R2160=50kohm(IN+ connected to GND through 50kohm), PIN25=PIN23=1.6V, Vout=8V.
    

    We don't understand why different R2160 will affect Vin and Vout.
    

    We expect them to be 0V since PIN25 is pulled to GND through no matter how big resistor.
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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