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AD5941 Recommended for New Designs
The AD5940 and AD5941 are high precision, low power analog front ends (AFEs) designed for portable applications that require high precision, electrochemical...
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The ADG636 is a monolithic device, comprising two indepen-dently selectable CMOS single pole, double throw (SPDT) switches. When on, each switch conducts...
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CN0510: Handling Battery with Higher Voltages



		

			

									
					    wklee
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 7, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  AD5941 
    
    		        		        		        
    Software Version: N/A
    
    		    		    	
			
    Dear Analog Devices Engineers,
    

    I am currently studying the possibility to convert the design described in CN0510 circuit note to handle batteries that have higher voltages, for EIS purposes (measure battery impedance). Typical example would be 12V battery, which I think not supported in the current evaluation board (EVAL-AD5941BATZ).  According to the circuit diagram from EVAL-AD5941BATZ, the excitation signal was generated through the pin CE0, which drives the Darlington transistor pair, connected to a battery. This topology directly draws the current from the battery under test, I am not sure how many V can it takes. I think that it probably cannot support a battery up to 12V. Is there any way we can develop a solution to measure batteries with 12V or even higher?
    

    My guess is that we would need to design another type of switching circuit rather than using Darlington transistor pair.
    

    Thanks.
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 hardware
                
                                                    
                 ad5941
                
                                                    
                 Sensors and MEMS
                
                                                    
                 ADG636
                
                                                    
                 impedance
                
                                        
                                            
                
                
                                        
                                            
                
                
                                        
                                            
                
                
                                
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        Anyone can reply this question? Thank you in advance.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        •  Super User  
        
            
			                            
                                                                                                                        
            
				
			
            
												
						in reply to wklee
					
									
        
	
        

		
		
        
					
        Hi  ,
        

        Apologies for missing this item. We will look into this. I will contact the product owner and get back to you.
        

        Regards,
        

        JC
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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        Hi,
        

          TIP31BG is used in the Darlington pair which allows VCE upto 10V (since its Vcc = 10V). For batteries with 12V, some other power transistor with VCC >=12V must be used for the Darlington pair.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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						in reply to Akila
					
									
          
	
          

		
		
          
					
          TIP31A - Complementary Silicon Plastic Power Transistors (onsemi.com)
          

          Says TIP31BG can stand max of 80 VDC. 12 should be no problem. No?
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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						in reply to kpjamro
					
									
          
	
          

		
		
          
					
          Hi,
          

            

          • The TIP31BG is an 80V device, so that’s one limitation.
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          • The limit is the voltage ratings on capacitors C36/37/38/39 used in EvalAD5940BATZ board which are 10V devices.
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          Hence VCE voltage is restricted to 10V max.
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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						in reply to Akila
					
									
            
	
            

		
		
            
					
            OK - although those caps are effectively connected in series and might take 20 volts.  Looking at it, I now wonder about the ADG636. The absolute max input voltage is specified as VDD +0.3 volts. During connection or disconnection of a battery, it might see a momentary spike as high as the battery terminal voltage. Is there any built-in protection for this? 
            
			
            

		
			
	      

		
		
	
            
	
            
		
            
			
		
            
	
            
	
            
		
						
				
				
						
				
				
		
		
            
			
		
            
	
            

            

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						in reply to kpjamro
					
									
            
	
            

		
		
            
					
            There is a low pass filter (marked by LPF0 in schematic) at the input of ADG636 that doesn't allow spike voltage to reach the IC.
            

            Yoi may refer to EVALAD5940BATZ schematic here: CN0510 User Guide [Analog Devices Wiki] for circuit at input of ADG636.
            
			
            

		
			
	      

		
		
	
            
	
            
		
            
			
		
            
	
            
	
            
		
						
				
				
						
				
				
		
		
            
			
		
            
	
            

            

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              Sorry. I don't see how this protects the 636.  I can understand that this prevents sustained voltage from appearing at "sense_p" but it seems to me that C39 and R2 actually form a high pass filter that would provide a nice transient into pin 11 of the 636.
              

              The situation I am thinking of is where F- S- are connected to the battery (and hence AGND) and then you connect S+ F+..  The point SNS_P momentarily rises to the full battery voltage relative to AGND.  As C9 and C36 charge up, this voltage difference decays.
              

              I think the only thing that protects against this is the 1K resistor R8 and any built-in protection diodes on the inputs of the 636. Looking at the spec sheet, I see that there are supposed to be such diodes. Max current spec is 20 ma for 1 ms. So perhaps the inputs are protected up to about 20 volts. 
              
			
              

		
			
	      

		
		
	
              
	
              
		
              
			
		
              
	
              
	
              
		
						
				
				
						
				
				
		
		
              
			
		
              
	
              

              

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						in reply to kpjamro
					
									
              
	
              

		
		
              
					
              I am telling about the LPF0 wire connected to input of ADG636, not the series cap.
              

              You may search for LPF0 in schematic. 
              
			
              

		
			
	      

		
		
	
              
	
              
		
              
			
		
              
	
              
	
              
		
						
				
				
						
				
				
		
		
              
			
		
              
	
              

              

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						in reply to Akila
					
									
                
	
                

		
		
                
					
                In the schematic that I have, there is no connection from LPF0 to ADG636.
                

                

                 
                

                Perhaps you mean via 2.2 Meg resistors R2 and R3?  
                
			
                

		
			
	      

		
		
	
                
	
                
		
                
			
		
                
	
                
	
                
		
						
				
				
						
				
				
		
		
                
			
		
                
	
                

                

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