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MAX25520 Production
The MAX25520 is a dual-output power IC that provides symmetrical or asymmetrical positive and negative voltages up to 10.5V and down to -10.5V (±12V for...
Datasheet
MAX25520 on Analog.com

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Feed forward capacitor requirement

		
	
				

			

									
					    jannerfish
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Apr 23, 2025 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  MAX25520  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Datasheets sometimes mention that supply transients can be removed and output ripple can be improved by the addition of a feed-forward capacitor, Cff.
    

    Is there any benefit to using Cff across R1 (betwwen AVDD and FBP) in the MAX25520?
    

    What might be a suitable value for Cff with R1 = 169k, R2 = 16k2 ?
    

    

     
    
			
    
			
									
		                             
                        

    
    
                                            
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                 PMIC and Multifunction
                
                                                    
                 Multitopology DC/DC
                
                                                    
                 ripple
                
                                                    
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                on Apr 24, 2025 2:36 AM
            
            
						
			            		
        
		
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        This is for the MAX 25520 with switching frequency, Fsw = 2.1 MHz.
        

        

        Also, I've seen that the feed-forward capacitor value Cff can be estimated using the crossover frequency as 1/10 of the switching frequency.  So,
        

        

        Cff = 1 / [ 2*pi*R1*(Fsw/10) ]
        

        Cff = [ 1.6 / R1*Fsw ]
        

        

        is this reasonable?
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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