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AD698 Production
The AD698 is a complete, monolithic Linear Variable Differential Transformer (LVDT) signal conditioning subsystem. It is used in conjunction with LVDTs...
Datasheet
AD698 on Analog.com

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AD 698 Operation



		

			

									
					    GHartl289
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 23, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hello Everybody,
    

    

    I have some questions regarding the operation of the AD698.
    

    At first, the datasheet tells us something about the excitation output characteristics at the certain frequency of 2.5 kHz.
    

    How do they change over frequency, as I want the AD698 to generate a sine wave with 16.9 kHz? It is also mentioned, that the Output Current is a minimum of 30 mArms.
    

    When I choose R1 to be around 6-8 kOhm and therefore the Excitation Voltage to be around 5 Vrms, the Simulation of the Spice-Model of my Sensor Circuit calculates a current through the primary coil of approx. 25 mArms, which is lower. What will happen, when I run the LVDT with this configuration? Or should I choose to operate the LVDT with a higher voltage amplitude to be in the range of 30 to 50 mArms?
    

    

    The second part of my question considers the power consumption of the AD698. Because of various reasons want to read in the sensor signal with the TIVA-Board (TM4C123GXL) from TI. Therefore I was thinking of powering the AD698 via the TIVA-Board, which has a 5V-DC output, using a Switching-Mode-Regulator from 5V to +-15V (like the MAX743). My first thought was to estimate the effective power of the exciation output and the signal output of the IC, but do I have to take more into account?
    

    

    Thank you and best regards,
    

    Georg
    
									
			        
		
    

				
						
        

    
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      •  Analog Employees  
      •  Super User  
      
            
						
                            
            
            				
            
                on Jul 23, 2021 7:47 AM
            
            
					
      
	
      

		
		
      
					
      Georg,
      

      Can you please be more specific about the characteristic(s) of interest you wish to understand at 16.9KHz?  This will help me assist you more efficiently.
      

      I will answer the rest of your queries below.
      

      GHartl289 said:
      It is also mentioned, that the Output Current is a minimum of 30 mArms.
      

      This is the minimum guaranteed output current, no a minimum allowed.  If your sensor will only consume 25mArms from the output you will not have any issues.
      

      GHartl289 said:
      Therefore I was thinking of powering the AD698 via the TIVA-Board, which has a 5V-DC output, using a Switching-Mode-Regulator from 5V to +-15V (like the MAX743). My first thought was to estimate the effective power of the exciation output and the signal output of the IC, but do I have to take more into account?
      

      You should be able to do this but the total power consumed by the device will be 18mA + your excitation load current.  So you are going to be close to consuming 45mA or so across 30V or about 1.3W.   The 5V rail on your TIVA board looks to be rated to about 1.5W so with the efficiency of the switching regulator you might be close to the limit of what the board can supply, especially given I don't know what load you have on the 3.3V rail.
      

      Sean
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      •  Super User  
      
            
						
                            
            
            				
            
                on Jul 23, 2021 7:47 AM
            
            
					
      
	
      

		
		
      
					
      Georg,
      

      Can you please be more specific about the characteristic(s) of interest you wish to understand at 16.9KHz?  This will help me assist you more efficiently.
      

      I will answer the rest of your queries below.
      

      GHartl289 said:
      It is also mentioned, that the Output Current is a minimum of 30 mArms.
      

      This is the minimum guaranteed output current, no a minimum allowed.  If your sensor will only consume 25mArms from the output you will not have any issues.
      

      GHartl289 said:
      Therefore I was thinking of powering the AD698 via the TIVA-Board, which has a 5V-DC output, using a Switching-Mode-Regulator from 5V to +-15V (like the MAX743). My first thought was to estimate the effective power of the exciation output and the signal output of the IC, but do I have to take more into account?
      

      You should be able to do this but the total power consumed by the device will be 18mA + your excitation load current.  So you are going to be close to consuming 45mA or so across 30V or about 1.3W.   The 5V rail on your TIVA board looks to be rated to about 1.5W so with the efficiency of the switching regulator you might be close to the limit of what the board can supply, especially given I don't know what load you have on the 3.3V rail.
      

      Sean
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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