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AD5658R Output Voltage Range



		

			

									
					    dnld
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 16, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hello,
    

    I am prototyping with the AD5658R DAC and I have it assembled as recommended in the quick start guide with a few exceptions.
    

     
    

    The device is powered with 5V. VLogic is tied to 3.3V. GAIN is tied to VLogic(3.3V) and RSTSEL is tied to 3.3V as well.
    

    On testing the device with GAIN of 1(GAIN tied to GND), I have confirmed the range is between 0V and 2.5V.
    

    However, after setting GAIN to 2(GAIN tied to 3.3V), the range seems to go between 2.5V and 5V. I am expecting a unipolar output from 0V to 5V as stated in the datasheet, but the  result is not the case.
    

    Is there something I may be missing? Any help to figure out the problem is appreciated. Thanks!
    
									
			        
		
    

				
						
        

    
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      •  Analog Employees  
      •  Super User  
      
            
			                            
                                                                                                                        
            
				
			
            
												
						in reply to dnld
					
									
      
	
      

		
		
      
					
      Hi, 
      

      Does that mean when you're sending a zero scale command 0x0000 to the DAC input registers, the output is at 2.5Vinstead of 0V? When you trigger a hardware reset using the reset pin at gain=2, the output is at what voltage? it'd be at midscale (2.5V) since your RSTSEL is high, if you set it low and do a reset, the output should be 0V right?
      

      There might be something we need to check on your serial interface. Are you sure you're following the SPI timing diagram in the datasheet? AD5686R/AD5685R/AD5684R (Rev. E) (analog.com)
      

      Could you get a scope shot of your SCLK, SDIN, SYNC signals?
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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						in reply to iandal
					
									
        
	
        

		
		
        
					
        That's correct, when I send 0x0000 to the DAC input registers, the output is 2.5V.
        

        When a hardware reset is triggered at GAIN=2, the output is at 2.5V.
        

        I have just set GAIN to 1(GAIN tied to ground) and can confirm that when i send the 0x0000 it outputs close to 0V and when i send 0xFFFF it outputs 2.5V. However, anything between 1-2.3 V will output a random value between 1.8V to 2.44V.
        

        In this example I send 0x947B, which is decimal for 38011 and a voltage output of 1.45V based on the transfer function, but the DAC outputs 1.87V. In another case, i send 0xA8F6, the decimal for 43254 and a voltage output of 1.65V, I am getting 2.44V out of the DAC.

         

        


         
        

        Any help is appreciated, thanks!
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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