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LT1254 Production
The LT1253 is a low cost dual current feedback amplifier for video applications. The LT1254 is a quad version of the LT1253. The amplifiers are completely...
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LT1254 on Analog.com

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LT1254 - rail consumption (unconnected OPAs)

		
	
				

			

									
					    Anja
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 19, 2021 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Hi,
    

    I am using only one OPA within LT1254 (the connection was tested in LT Spice enviroment and was working there). For the remaining 3 OPAs I connected + to GND, - and OUT together with a 620E resistor. The + IN of used OPA is driven with either + or - 4.5V, while the rail voltages are +10V and -5V. The rail current limitation used is 100mA causes the positive rail to drop to 4V. The chip operating temperature during testing is 35°C.
    


    Do you have any idea what would be the issue for such a consumption?
    

    

    Best regards, 
    

    Anja
    
			
    
			
									
		                             
                        

    
    
                                            
                 Operational Amplifiers (Op Amps)
                
                                                    
                 amplifiers
                
                                                    
                 opamp
                
                                                    
                 Low Noise Op Amps (= 10nV/vHz)
                
                                                    
                 rail consumption
                
                                        
                                            
                
                
                                
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Oct 21, 2021 3:27 PM
            
            
						
			            		
      
		
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      The unused sections should be ok as you described, but the feedback resistance could be increased some to reduce the loop gain and help avoid UHF oscillations that can draw a lot of current (good RF layout with supply bypass caps as close as possible to the IC are needed to prevent oscillation in general).  I assume the used opamp also has a feedback resistance. As a CFA type opamp, the -IN will follow the +IN so any gain resistor may draw a lot of current with 4.5V of drive. CFA's also can draw lots of current if driven into saturation due to the internal current gain. Also note any load current, for example 4.5V/50R is nearly 100mA and would overstress a section.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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