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LTC4222 Production
The LTC4222 Hot Swapâ„¢ controller allows two power paths to be safely inserted and removed from a live backplane. Using external N-channel pass transistors...
Datasheet
LTC4222 on Analog.com

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LTC4222 GPIO sink current

		
	
				

			

									
					    lukaskn
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 20, 2022 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  LTC4222 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi,
    

    We're using the LTC4222 Hotswap Controller. What is the maximum sink current for its GPIO pins and what happens beyond that? If trying to sink too much current, would you expect the Hotswap to work in all other regards but the GPIO?
    

    The background: one of the GPIOs is used to delay the configuration of an FPGA. As long as GPIO=0, the FPGA shouldn't configure. When GPIO=1, the FPGA starts to configure. Unfortunately, after configuring, the FPGA drove this GPIO high. If now the LTC4222 got an external I2C command to bring the GPIO=0, the FPGA and the Hotswap are fighting each other. As I am seeing issues with this delayed configuration and I don't have direct physical access to the board, I am tried to estimate what might have happened and if FPGA and/or LTC4222 got damaged.
    

    

    Thank you very much and best regards
    

    Lukas
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 22, 2022 4:48 PM
            
            
						
			            		
      
		
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      Lukas,
      

      

      The maximum sink current for the GPIO is not specified on the datasheet. It assumed that the current is limited by a pull-up resistor.
      

      The datasheet provides this:
      

      

       
      

      

      From this graph we can determine that the GPIO output has an RDSon of approximately 50 Ohms.
      

      I do not know how much current the FPGA can source. If the current is too high the dissipation in the FET may damage the GPIO pin or the FPGA.
      

      Can you place a resistor, in series, between the GPIO pin and the FPGA?
      

      

      JayBee
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
				
				
				
		
		
      
			
		
      
	
      

      

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                on Jul 25, 2022 10:11 AM
            
            
												
						in reply to JayBee
					
										
			            		
        
		
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        Dear Jay,
        

        

        Thank you for the response which was quite insightful. The FPGA should be able to source 24mA, although I did not constrain any specific driving current, so with its default, its probably 12mA.
        

        Of course, you can not give a conclusive answer on this, but if the LTC4222's FET was damaged, would you suspect any further damages for the LTC4222?
        

        I actually have a resistor between the LTC and the FPGA, but - of course - it's assembled with 0 Ohms. What would you intend with it (expect of improving a later revision)?
        

        

        Cheers
        

        Lukas
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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