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AD8557 Recommended for New Designs
The AD8557 is a zero drift, sensor signal amplifier with digitally programmable gain and output offset. Designed to easily and accurately convert variable...
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AD8557 on Analog.com

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AD8557 analogue and digital supply voltage and communication

		
	
				

			

									
					    Ledeir
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Nov 16, 2021 
				
			
			
		

		
		                     
				
        		

		    
		    		    
		    			

			    
Dear all,




I am currently trying to develop a PCB circuit using AD8557 to amplify a wheatstone bridge. However, I have some questions regarding the supply voltages and communication voltages. I am connecting the amplifier to a board that outputs 3.3V on digital pins. So, my question is, 


According to the AD8557 datasheet one can use AVDD and DVDD as supplies. If I set the excitation voltage of the bridge as 5V, the AVDD = 5V and DVDD = 3.3V, when trying to configure the AD8557 gain and offset, will it work? Since the microcontroller board outputs 3.3V in the digital pins?
What if I set the AVDD=DVDD=5V, will I be able to configure the AD8557 in simulation mode, using 3.3V TTL?




Thanks in advance!

			

			
									    

			        
Edit Notes

    				added excitation voltage

[edited by: Ledeir at 2:33 PM (GMT -5) on 16 Nov 2021]
				

						
		                             
                        

    

                                            
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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Nov 22, 2021 2:06 AM
            
            
						
			            		
    
		
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    Hi Ledeir,
    

    Thank you for checking out our product for your application.
    On your first scenario with AVDD=5V and DVDD = 3.3V, the AD8557 should be able to detect the microcontroller's high and low GPIO output without a problem. Most of the details on the datasheet is with regards to the SOIC package but I would think that on the LFCSP package DVDD is independent with the AVDD and corresponds to the digital interface.
    

    Unfortunately, on your second scenario where AVDD=5V and DVDD=5V while still using the 3.3V microcontroller output. Looking at the specification table on the digital interface section:
    

     
    

    The DIGIN Low and DIGIN High is ratiometric with regards to the Digital Supply of the chip. Meaning if DVDD = 5V, DIGIN High must be at least 4V for it to recognize the GPIO's Logic High.
    

    One more thing to take note of when blowing the fuse you need to have 5.75V supply according to the Programming Mode section within the datasheet.
    

     
    

    Hope this helps.
    

    Best Regards,
    Dann
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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