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LT1308 Production
The LT1308 is a micropower, fixed frequency boost DC/DC converter that operates from an input voltage as low as 1V. Capable of delivering 5V at load current...
Datasheet
LT1308 on Analog.com

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LT1308 and SHDN pin operation

		
	
				

			

									
					    AMDerek
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 2, 2023 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  LT1308 
    
    		        		    		    
    
		    		    
		    			
    
			    
    

    I am looking at the LT1308 PWM boost controller. Per the datasheet, it says that SHDN should be 1V to 10V. I have a circuit configuration where the output can vary based on the input, but my input can be below 1.0V. Thus, tying SHDN to the input allows the circuit to start up at 1.0V. However, if I tie the SHDN to the input with a 10k resistor, would this be sufficient to start up at 1V?
    

     
    

    As a follow-up question, I would like to tie SHDN to the output (varys up to 9V) while still having the 10K resistor to the input. Now, how low can the input be for the LT1308 to still function since the SHDN will be getting a voltage from the output (>1V)?
    

    
			
    
			
									
		                             
                        

    
    
                                            
                 power management
                
                                                    
                 hardware
                
                                                    
                 Step-Up (Boost) Regulators
                
                                                    
                 switching regulators
                
                                                    
                 LT1308
                
                                        
                                            
                
                
                                        
                                            
                
                
                                
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                on Oct 2, 2023 2:14 PM
            
            
						
			            		
        
		
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        OK, I did some testing. 
        1. Connecting pin 3 to a 10k to Vin does not affect start up.
        2. Connecting pin 3, also, to Vout does affect operation by lowering the output voltage. I am sure it is because the circuit is attempting to draw power through the 10k resistor. Though, it does not make sense to see a significant drop in the output.
        2-followup. I can connect to 100k and no effect on output, however it does still shuts down below 1.0Vin.

        I did try to connect pin 3 to 2V and then lower Vin below 1.0V. LT1308 shut itself down as if pin 3 was connected directly to Vin. Must be an internal UVLO on the Vin; spec does have a minimum input voltage of 0.92V (though I see the drop out around 0.98V).
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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