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LTC3567 Production
The LTC3567 is a highly integrated power management and battery charger IC for Li-Ion/Polymer battery applications. It includes a high efficiency current...
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LTC3567 on Analog.com

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LTC3567 VOUT1 Voltage Setting



		

			

									
					    James@Techne
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 12, 2020 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi, 
    

    I'm not seeing the intended output voltage from the VOUT1 (Buck-Boost Regulator) on my LTC3567. The schematic is attached. It's a pretty vanilla application, very similar to the example applications in the datasheet. Could I get a quick verification that the schematic is at least correct?
    

    I've already gone through my board and checked for shorts and opens and everything seems to be physically connected according to the schematic.I currently don't have a battery attached because I'm still going through board bring up.

    VOUT1 goes to a current sense resistor (+3.3V_SNS) and the +3.3V rail is on the other side of that current sense resistor, which the FB1 pin is biased from. 
    

    I temporarily tied the EN1 pin to VOUT (which I've measured to be 3.6V) to enable the buck-boost converter, since I don't currently have a battery attached it seems the default setting is for the VOUT1 to be OFF according to the default 0xFF00 value in the control register.
    

    The datasheet mentions that "the switching regulator delivers power until the CLPROG pin reaches 1.188V." I measured the voltage at the CLPROG and it was only at 0.3V  
    

    

    Any help for a sanity check would be appreciated. Thanks!
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 battery management
                
                                                    
                 LTC3567
                
                                                    
                 PMIC (DC/DC  PowerPath  and Battery Charger)
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Nov 13, 2020 2:47 PM
            

            
					
      
	
      

		
		
      
					
      Hello, Thank you for the information. The only thing I noticed is the schematic does not show an output capacitor on VOUT1. This should have at least a 10u. A 22uF will match the app on page 27 of the datasheet that uses the same compensation. 
      

      Does VOUT droop when VOUT1 is enabled or does it stay at 3.6V? With CLPROG at 0.3V I would expect VOUT to be pretty steady.
      

      Have you looked at VOUT and VOUT1 with an oscilloscope?
      

      Is the battery charger disabled? If not is there an RC for stability on the battery pin as suggested on in the Battery Charger Stability Considerations section of the datasheet on page 26?
      

      Thanks
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Nov 13, 2020 2:47 PM
            

            
					
      
	
      

		
		
      
					
      Hello, Thank you for the information. The only thing I noticed is the schematic does not show an output capacitor on VOUT1. This should have at least a 10u. A 22uF will match the app on page 27 of the datasheet that uses the same compensation. 
      

      Does VOUT droop when VOUT1 is enabled or does it stay at 3.6V? With CLPROG at 0.3V I would expect VOUT to be pretty steady.
      

      Have you looked at VOUT and VOUT1 with an oscilloscope?
      

      Is the battery charger disabled? If not is there an RC for stability on the battery pin as suggested on in the Battery Charger Stability Considerations section of the datasheet on page 26?
      

      Thanks
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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                on Nov 13, 2020 3:15 PM
            

            
												
						in reply to MartyM
					
									
        
	
        

		
		
        
					
        Yes, VOUT1 does not have a dedicated output capacitor. I've marked that as a change for the next revision.VOUT1 does have a capacitor on the other side of the current sense resistor, but it's not directly connected to VOUT1.
        

        I tempted fate by putting some 0201 capacitors a little too close to each other to decouple some internal LDOs for the processor on the board. The soldermask wasn't quite thick enough and the caps got shorted together. I was testing the board by powering it through USB and the current was being limited. I tried powering through the battery connection with a bench power supply and was able to manually set the current limit. That solder bridge wasn't shorting the power rails, but it was drawing a significant amount of current.
        

        I was able to remove one of the caps and fix the solder bridge and now I'm measuring the current voltage VOUT has 3.3V as intended. But I need to confirm on another board that that was the solution. I'm waiting on some better tools to rework some 0201 caps to arrive in the mail.
        

        I did look at VOUT1 with an oscilloscope and there was a significant ripple, maybe +/- 0.25V.
        

        The battery charge is currently disabled.
        

        Thanks for the quick review! I'm 90% sure that my board was trying to draw too much current causing VOUT1 to sag, but I'll confirm when I'm better equipped to rework those 0201 caps on another test board.
        

        

        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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