Products Mentioned

AD8646 Production
The AD8646 and the AD8647 are the dual, and the AD8648 is the quad, rail-to-rail, input and output, single-supply amplifiers featuring low offset voltage...
Datasheet
AD8646 on Analog.com

AD8648 Production
The AD8646 and the AD8647 are the dual, and the AD8648 is the quad, rail-to-rail, input and output, single-supply amplifiers featuring low offset voltage...
Datasheet
AD8648 on Analog.com

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Replacing LMV84x by AD8646/8648 ?



		

			

									
					    usaghi
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on May 8, 2015 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    
 
    We are now studying to replace LMV84x on existing system by AD8646 or AD8648, then having questions as follows.
    
 
    1) Absolute Maximum Ratings of input voltage at AD8646/8648 is defined as "GND to Vsy".
    
 
      I could not find any clear definition in the datasheet what is Vsy, but assuming it has to be Supply Voltage, from analogy of Isy defined as Supply Current Per Amplifier.
    
 
      Is this true ? Correct me if wrong.
    
 
    2) When using AD8646/8648 at 5V single supply, however input voltage can be the rage from  -(minus)0.3 to 0V.
    
 
      It seems out of range defined on Absolute Maximum Ratings in the datasheet, so is it not available to use, even if it is only an instant of eye blink ?
    
 
      Please make sure if it is correct.
    
 
    3) LMV84x is RRin and RRout, 5V single supply but it is still available to  -(minus)0.3V input voltage.
    
 
      I looked for the same ADI parts and found AD8607/AD8609, but their GBP is around 300KHz, and we need a few MHz bandwdth.
    
 
      Could you provide other ADI parts which fullfill above conditions (R-R in, R-R out, single supply 5V,  -0.3~0V input voltage, GBP=a few MHz) ? 
    
 
      Hopefully Vos (Offset Voltage) is a few handreds uV range and Ib (Bias Current) is around 1pA, not to be far outweighed by LMV84x. 
    
 
    Best Regards,
    
 
    Usaghi
    
									
			        
		
    

				
						
        

    
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                 Operational Amplifiers (Op Amps)
                
                                                    
                 amplifiers
                
                                                    
                 ad8646
                
                                                    
                 ad8648
                
                                                    
                 Low Noise Op Amps (= 10nV/vHz)
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on May 11, 2015 8:46 PM
            
            
					
      
	
      

		
		
      
					
      Hi Usaghi,
      
 

      
 
      Regarding to your first question,  you're right about Vsy and Isy. Vsy or simply Vs, is the supply voltage of the part while Isy is the supply current per amplifier of the part. 
      
 

      
 
      On your second question, actually our parts has input over-voltage protection diodes. However, it is not guaranteed that the part will not be damaged from overstressing the input. That's the reason why we have limits on the spec table to ensure the performance of the part within the limits. You may also try to read this tutorial about input over-voltage protection: http://www.analog.com/media/en/training-seminars/tutorials/MT-036.pdf
      
 

      
 
      I suggest the AD8691 part. At a supply voltage of 5V, it has an input voltage range of -0.3V to 3.9V. It is a rail-to-rail output amplifier, has a GBP of 10MHz, has a typical input offset voltage of 400uV and has a typical input bias current of 0.2 pA. You may also try to look at ADA4691 part.
      
 

      
 
      Can I ask what is your application?
      
 
      I hope this helps!
      
 
      Regards,
      
 
      Jay
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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    • 
	
      



	
			
		
	



      
	
      
		
      
							
					
      
		
      
			
													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on May 11, 2015 8:46 PM
            
            
					
      
	
      

		
		
      
					
      Hi Usaghi,
      
 

      
 
      Regarding to your first question,  you're right about Vsy and Isy. Vsy or simply Vs, is the supply voltage of the part while Isy is the supply current per amplifier of the part. 
      
 

      
 
      On your second question, actually our parts has input over-voltage protection diodes. However, it is not guaranteed that the part will not be damaged from overstressing the input. That's the reason why we have limits on the spec table to ensure the performance of the part within the limits. You may also try to read this tutorial about input over-voltage protection: http://www.analog.com/media/en/training-seminars/tutorials/MT-036.pdf
      
 

      
 
      I suggest the AD8691 part. At a supply voltage of 5V, it has an input voltage range of -0.3V to 3.9V. It is a rail-to-rail output amplifier, has a GBP of 10MHz, has a typical input offset voltage of 400uV and has a typical input bias current of 0.2 pA. You may also try to look at ADA4691 part.
      
 

      
 
      Can I ask what is your application?
      
 
      I hope this helps!
      
 
      Regards,
      
 
      Jay
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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