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Ltc3260 noise reduction

		
		

		

			

									
						gZoppi550
					
							

			
				
									
											
			        
                                                			
				
			
		


				
		

		    
		    
		    		    
			
Hello, 


I am involved in  the design  of the amplifying and clipping section of a guitar audio processor embedding your Ad528x digipots. For that a dual supply +-5V is necessary and we are currently exploiting (in the first working prototype)  the LTC3260


The involved circuit has a very high gain, so, having the cleanest supply is mandatory.


What appears upping the gain is that  the switching noise is somehow downconverted thus generating an audible tone which is unwelcome especially when the instrument is not playing.


The switching noise is present at both positive and negative rails.


Do you have any suggestion ? Maybe exploiting an lc filter with snubber?


Is there any additional solution with different PN that might fit our needs?


 




 




Thanks in advance for your support.


BR


GZ

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	










	

	

					



			


				
	









	
    
	

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    Hello, it seems that the input voltage is too low for the configuration with the external diode divider. I will try upping a bit the input voltage andbthen I will change configuration removing the divider.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

    

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						in reply to gZoppi550
					
									
    
	
    

		
		
    
					
    Update: after restoring the configuration  without diode divider nothing changes: at high gain the switching noise is clearly present. 
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

    

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						in reply to gZoppi550
					
									
    
	
    

		
		
    
					
    Hello, A couple things that might need to be done to reduce the noise. First look at the layout. Make sure there is an adequate GND plane, the input, flying, and output caps are close to the IC with a good path to GND. Make sure there are no sensitive nodes or components near any of the switching components and all sensitive returns are not in the path of the switching return paths or input cap return to the IC paddle. 
    

    If the 12V input is shared with other sensitive components a conductive EMC π filter using ceramic caps and a ferrite bead with help reduce any noise feeding back from the input. 
    

    Using ceramic caps with low ESL and low ESR will help reduce the spikes. Smaller packages have lower ESL and using as small of a package that will allow the proper capacitance can help. 
    

    If needed another π filter on the outputs might also be needed.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    

    

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