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LTC3871 Recommended for New Designs
The LTC3871/LTC3871-1 is a high performance bidirectional buck or boost switching regulator controller that operates in either buck or boost mode on demand...
LTC3871 on Analog.com

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LTC3871 - HV system application

		
	
				

			

									
					    flasz
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 17, 2023 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  LTC3871 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi,
    

    I am looking into possibility of using LTC3871 as a bidirectional current controller in a higher than recommended voltage system (800V and around 200V). My main concern are inductor current sense channels, since they are optimized for direct shunt connection with range limited to ~50 mV. Are there any recommendations for current sensing circuit in such application? My first thought was current transducer with FDA circuit scaling transducer reading to appropriate range or isolation amplifier combined with FDA conditioning.
    

    Is there anything I should also pay special attention to while using LTC3871 in this way? Or maybe LTC3871 is not suitable for this application? I was also planning to connect 2 LTC3871 to create 4-phase interleaved system.
    

    Thank you in advance,
    

    BN
    
			
    
			
									
		                             
                        

    
    
                                            
                 hardware
                
                                                    
                 High Input Voltage Buck Regulators
                
                                                    
                 LTC3871
                
                                                    
                 Step-Down (Buck) Regulators
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jan 5, 2024 10:24 AM
            
            
						
			            		
      
		
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      Hello BN,
      

      VHIGH and VLOW voltages of 800V and 200V are too high for the LTC3871 as you noted. The 800V VHIGH limitation can be circumvented by biasing the LTC3871 with an external bias of 12V, preferably, and external gate drivers. However, 200V on VLOW presents a difficult challenge. The maximum VLOW voltage of the LTC3871 is 30V since the absolute maximum rating of its current sense pins is 34V. Using a resistor divider to drop the common mode voltage to 30V or below is not possible due to the 1.5mA input current of the SNS- pins and the large attenuation factor required (>7x). Using a high voltage difference amplifier may be a solution. However, the BW of the amplifier should be about 10x the switching frequency to allow the triangular portion of the current sense waveform to pass through. Otherwise, the current sense signal will be rounded and delayed. This can lead to stability issues. Since the LTC3871 is a peak current mode controller, the current sense signal is a critical part of the feedback loop. If you still need assistance with this circuit, then contact your local FAE.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
				
				
				
		
		
      
			
		
      
	
      

      

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