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ADT6401 Production
The ADT6401/ADT6402 are trip point temperature switches available in a 6-lead SOT-23 package. Each part contains an internal band gap temperature sensor...
Datasheet
ADT6401 on Analog.com

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ADT6401 Output Problem

		
	
				

			

									
					    Feanor
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on May 14, 2012 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user is experiencing incorrect operation of ADT6401 temperature switches on their board, which shut down the board at room temperature. The issue is due to the part not entering the correct mode when the Vcc rise time is greater than 10ms, causing floating inputs to be misinterpreted as GND. The user tested the ADT6401 and found that it checks its inputs 2.5ms after power-up, leading to incorrect latching of input states with slow Vcc rise times. A potential alternative is the ADT6501, which has factory-set trip points in a similar package.
                        	    
    
                
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    Hi,
    
 
    We are using two ADT6401 temperature switches on our board. They are open-drain output. We use one for the high temperature (+85 degrees celcius) and one for the low temperature (-45 degrees celcius). Our schematic is attached. 
    
 

    Temperature switches can shutdown our board. While we are testing the board at room temperature, our board shuts down because one of the temperature switches pulls their output low. We could not understand which of them. But the temperature is very far away from both high and low limits. So temperature switches do not operate correctly, that's for sure.
    
 
    Our low temp. switch inputs are Float - GND - Float. If the float on the S2 pin, is measured as GND some time, the temperature setting goes to +65 degrees celcius. Could this be a problem? Or could it be a soldering effect?
    
 
    Thanks,
    
 

    Celil
    
			
    
			
									
		                             
                        

    
    
                                            
                 temperature
                
                                                    
                 sensor
                
                                                    
                 adt6401
                
                                                    
                 Temperature Sensor and Control Devices
                
                                                    
                 switch
                
                                        
                                            
                
                
                                
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                on May 14, 2012 3:05 PM
            
            
						
			            		
        
		
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        Hi again,
        
 
        - There are 100nF caps very close to the IC's (one for each). 
        
 
        - The output is pulled high to 4 volts with 100 uA current.
        
 
        To isolate the problem, we did some tests to the ADT6401 in a test board and we think we isolated the problem. Below are our findings:
        
 
        In the datasheet, ADT6401's operating supply voltage is given as 2,7 volts.
        
 
        1) 2,5 ms after powerup, ADT6401 checks its inputs (whether they are float, gnd, or Vcc)
        
 
        2) ADT6401 checks its inputs once and only once (2,5 ms after powerup).
        
 
        3) So, if anything goes wrong at powerup, the input states are latched.
        
 
        4) If Vcc rises slowly (1 volts per 25 ms), the float pins is not read correctly. They are read as GND's.
        
 
        So, in our case, 
        
 
        S2/S1/S0 (Float-GND-Float) (-45 degrees with 2 degrees hysteresis) becomes
        
 
        S2/S1/S0 (GND-GND-GND) (+45 degrees with 2 degrees hysteresis).
        
 
        We tested ADT6401 for 2 full days. We tested with scope. We know it checks its inputs 2,5 ms after powerup, because we measured the FLOAT pin and saw that it rises to half of Vcc 2,5 ms after powerup.
        
 
        That is very critical for us. We need to make sure that ADT6401 reads FLOAT state correctly independent of the rise time of Vcc.
        
 
        Please reply ASAP.
        
 
        Thanks and sincerely,
        
 
        Celil
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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      • 
	
        



	
		
	
	



        
	
        
		
        
							
					
        
		
        
		    
		    		    
			
				
									
							        
			
			
			
          
            
						
                            
            
            				
            
                on May 14, 2012 3:05 PM
            
            
						
			            		
          
		
										0
					
	
          

		
		
          
		
          
                                
                                                            
          
					
          Hi again,
          
 
          - There are 100nF caps very close to the IC's (one for each). 
          
 
          - The output is pulled high to 4 volts with 100 uA current.
          
 
          To isolate the problem, we did some tests to the ADT6401 in a test board and we think we isolated the problem. Below are our findings:
          
 
          In the datasheet, ADT6401's operating supply voltage is given as 2,7 volts.
          
 
          1) 2,5 ms after powerup, ADT6401 checks its inputs (whether they are float, gnd, or Vcc)
          
 
          2) ADT6401 checks its inputs once and only once (2,5 ms after powerup).
          
 
          3) So, if anything goes wrong at powerup, the input states are latched.
          
 
          4) If Vcc rises slowly (1 volts per 25 ms), the float pins is not read correctly. They are read as GND's.
          
 
          So, in our case, 
          
 
          S2/S1/S0 (Float-GND-Float) (-45 degrees with 2 degrees hysteresis) becomes
          
 
          S2/S1/S0 (GND-GND-GND) (+45 degrees with 2 degrees hysteresis).
          
 
          We tested ADT6401 for 2 full days. We tested with scope. We know it checks its inputs 2,5 ms after powerup, because we measured the FLOAT pin and saw that it rises to half of Vcc 2,5 ms after powerup.
          
 
          That is very critical for us. We need to make sure that ADT6401 reads FLOAT state correctly independent of the rise time of Vcc.
          
 
          Please reply ASAP.
          
 
          Thanks and sincerely,
          
 
          Celil
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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