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Original question:

TIDA-00854 application

TIDA-00854 for Amperometric electrochemical sensor

CHETAN RAWAT
Prodigy 130 points
Other Parts Discussed in Thread: TIDA-00854, LPV802

Hi. 

I was designing ozone gas sensor (using SPEC ozone sensor-20ppm) taking TIDA-00854 in reference. I am confused with the value of R2 and R5 which are 0 ohms. And about the RF.. can I use a large value (>4M)??  Removed Q1.. can I..???

It's there anything else that you would suggest to take care of..??

I can share my schematic of you want.. 

Thanks & Regards

C.R

  • 0
    TI__Intellectual 1160 points

    Hi Chetan,

    From the TIDA-00854 user and LPV802 datasheet, I think R2 and R5 are designed for testing or adjusting the Vref combined with R8 and R4, if you want change the reference voltage of your sensor while Vref is already fixed in the PCB.  R2 and R5 can be removed if the Vref of all your sensors are the same.

    About Rf, the value is mainly depending on the sensitivity of the sensor. The output rail of the amplifier should also be considered when choose the RF. You can find more details from the LPV802 datasheet, https://www.ti.com/lit/ds/symlink/lpv802.pdf

    As for Q1, I think it is specifically designed for the Gas sensor (CIty 4CF+). For some electrochemical gas sensor, the WE and RE are usually shorted to keep the sensor working when power off, avoiding drift. Q1 can be removed depending on your  electrochemical sensor system.

    Above are my own ideas according to the datasheet and user guide. I will check these with the Author and reply you. Hope my answers will help you and you can contact with me (matthew-chen@ti.com) if you got any question.

    Matthew Chen 

    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                 	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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                          Prodigy
                        130 points
                      
    
                          
                   		
		
    
					
    Hi Matthew.. 
    

    Thanks for your reply.
    

    Surely your answers had cleared most of my doubts.. 
    

    About RF, I wanted the output of the sensor to be 0-5V and spec sensor's sensitivity factor is 8nA/ppm and max range is 20ppm. So I calculated the RF according to th calculation shown in page 15 of the LPV802 datasheet. It came out to be 4.2Mohm. 
    

    I actually wanted to know whether LPV802 can support RF in Mega ohms..?? 
    

    Waiting for your reply..
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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						in reply to CHETAN RAWAT
					
									
    
	
    
	                                    
                      
    
                        
                          TI__Intellectual
                        1160 points
                      
    
                          
                   		
		
    
					
    Hi Chetan,
    

    For the RF, the upper value would be dominated by the input and sensor leakages. Resistor values are typically between 50k to 1M depending on the sensor sensitivity. 4M is not unreasonable, but you have to expect some drift and sensitivity at those levels.
    

    Please let me know if  you got questions.
    

    Matthew Chen
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                 	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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