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LTC1922-1 Production
The LTC1922-1 phase shift PWM controller provides all of the control and protection functions necessary to implement a high performance, zero voltage switched...
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LTC1922-1 on Analog.com

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LTC1922-1 ramp voltage



		

			

									
					    PhilinStLouis
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 12, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    On the LTC1922-1, what is the ramp voltage (pin 2) suppose to be?  
    Sawtooth right?  
    What is the voltage at the trough suppose to be? 
    What should the peak voltage be? 
    It should be the same frequency as Ct (pin 20) correct?  
    

    I'm using the 20pin DIP.
    

    My Ct is good, 3.8v peak,65Khz
    

    But Ramp (pin2) as only 0.2v peak on it. Have tried 100pf and 500pf on Ramp.  
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 LTC1922-1
                
                                                    
                 switching regulators
                
                                                    
                 Flyback  Forward  and Isolated Controller
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Oct 4, 2021 7:44 PM
            
            
					
      
	
      

		
		
      
					
      Yes, a sawtooth. 0.4V. Slope comp is typically set around 0.5 - 1 x the current downslope. I would use the minimum value for the Islp = 35uA, and pick a cap for a little more than 0.5x the current downslope signal. Same frequency.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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                on Oct 5, 2021 10:31 AM
            
            
												
						in reply to ADIApproved
					
									
        
	
        

		
		
        
					
        Do you mean the peak of the Ramp sawtooth should be 0.4Vpk? Why am I only getting 0.2v despite trying different caps? Are you saying the current source inside the chip is 35uA? At 100kz, a 875pf cap should achieve 0.4v in 10us. The smaller caps I tried should get to 0.4v sooner but they ramp to 0.2V, (not ramp to 0.2 and be flat after). The current must be less. Is there anything that could be reducing the 35uA? Does the voltage on Ramp pin trigger anything internally?         
        

        What should the trough on Ramp be? 
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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