Products In This Thread

ADP5585 Production
The ADP5585 is a 10I/O port expander with built-in keypad matrix decoder, programmable logic, reset generator, and PWM generator. I/O expander ICs are...
Datasheet
ADP5585 on Analog.com

  • State Verified Answer
  • Replies 5 replies
  • Subscribers 39 subscribers
  • Views 1411 views
  • Users 0 members are here
Options
Related 

        

            Post
             Go back to editing
        

    

    


    

    









		












	
	
			
	
			
			
	
	
		

		
ADP5585 going BAD after few days usage.ESD ISSUES?



		

			

									
					    jkmisra
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 1, 2016 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    We are using ADP5585 in our design for interfacing to a keyboard. The schematics is as shown in the attachment. The lines KBC0,1,2,3 and KBR0,1,2,3 are going to a 4 X 4 matrix KEYPAD connected with about 15 inches long ribbon cable. 
    
 
    The capacitors C2,C4,C6,C8, C67,C68,C69,C74 though are shown in schematics are not really mounted on board.
    
 
    The device TPD8F0003DQDR is being used as ESD protection device Its link is http://www.ti.com/lit/ds/symlink/tpd6f003.pdf
    
 
    we are noticing that in spite of using above ESD protection device we are seeing failures of the ADP5585 device. The failed devices basically have less than 50 ohm resistance between any of the I/O pins and GND. Incidentally we are seeing that even the lines which are not connected to KEYPAD like pin numbers 16, 10 and 1 which are connected to internal signals also develop this low resistance between that specific pin and GND.
    
 
    Also these failures Occur only after a few days of usage typically 5-10 days with KEYPAD being used about 10-15 times per days
    
 
    Following questions
    
 
    1. Has anyone else or even Analog devices have seen these kind of failures happening with ADP5585
    
 
    2. Is there any other issues in the schematics attached ?
    
 
    3. Is there really a ESD issue or is it for any other reason that the ADP5585 device may be going bad ?
    
 
    4. Should we use any other ESD protection device than the currently used ? probably the clamping voltage of the device we are using is little bit higher than the transient tolerance limit of ADP5585
    
								
    

							
    
				
				
			
    
					
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



Parents
	
      
	

    • 
	
      



	
		
	
	



      
	
      
		
      
							
					
      
		
      
			
													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                        
                on Mar 4, 2016 6:14 AM
            
            
					
      
	
      

		
		
      
					
      Hello,
      
 
      A. The abs. max for the row and column pins on the ADP5585 is -0.3V and (VDD + 0.3 V).
      
 
      
 
      Having excursions above this risk turning on internal body diodes, and repeated excursions can cause damage. These limits are very common as almost any CMOS design will have these body diodes in this configuration. If you scope very close to the part, the voltage excursions might be very hard to notice, as the body diodes will clamp the voltage to about these levels as they turn on. If voltage spikes are expected in a system, sometimes schottky diodes clamping input pins to VDD lines works to prevent this possible damage. The cathode of the schottky would be on VDD and the anode would be on the pin being protected. There can also be a schottky from the pin being protected to clamp to ground in case of a negative voltage.
      
 
      This probably isn't feasible in your final design, but it adding schottky diodes on all the row/col pins might help find the root cause of the failures.
      
 
      B. The ADP5585 was originally designed for very compact keypads with short distances between the keypad and the part. It was designed to not need external ESD devices in these cases. The ADP5585 works fine with longer cables, as long as the total line capacitance is low. If the capacitance is too high, the symptom would be multiple key presses being registered for single key press event, so it looks like your cables are fine capacitance-wise. The question is whether the long cables are somehow picking up voltage transients large enough to affect the part. The ESD structure you have right now does not have a clamping voltage low enough to prevent excursions above abs. max. One possible thing to try is putting 3.3V zener diodes on the row/col pins right near the part, anode on GND.
      
 
      B(C). The hypothesis about the chassis floating was about possible mechanisms that would cause voltage transients getting coupled in to the long cable lines. It is possible if the chassis ground were dramatically different than the system ground, and then they were shorted that a large spike would capacitively couple, but that is not very likely.
      
 
      These failures feel more like an over voltage situation than an ESD failure.
      
 
      Is the ESD protection very close to the ADP5585, or is it on the other side of the cables? Closer to the part is the best location.
      
 
      RSchnell
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

      • 

	
    



Reply

      


    • 
	
      



	
		
	
	



      
	
      
		
      
							
					
      
		
      
			
													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                        
                on Mar 4, 2016 6:14 AM
            
            
					
      
	
      

		
		
      
					
      Hello,
      
 
      A. The abs. max for the row and column pins on the ADP5585 is -0.3V and (VDD + 0.3 V).
      
 
      
 
      Having excursions above this risk turning on internal body diodes, and repeated excursions can cause damage. These limits are very common as almost any CMOS design will have these body diodes in this configuration. If you scope very close to the part, the voltage excursions might be very hard to notice, as the body diodes will clamp the voltage to about these levels as they turn on. If voltage spikes are expected in a system, sometimes schottky diodes clamping input pins to VDD lines works to prevent this possible damage. The cathode of the schottky would be on VDD and the anode would be on the pin being protected. There can also be a schottky from the pin being protected to clamp to ground in case of a negative voltage.
      
 
      This probably isn't feasible in your final design, but it adding schottky diodes on all the row/col pins might help find the root cause of the failures.
      
 
      B. The ADP5585 was originally designed for very compact keypads with short distances between the keypad and the part. It was designed to not need external ESD devices in these cases. The ADP5585 works fine with longer cables, as long as the total line capacitance is low. If the capacitance is too high, the symptom would be multiple key presses being registered for single key press event, so it looks like your cables are fine capacitance-wise. The question is whether the long cables are somehow picking up voltage transients large enough to affect the part. The ESD structure you have right now does not have a clamping voltage low enough to prevent excursions above abs. max. One possible thing to try is putting 3.3V zener diodes on the row/col pins right near the part, anode on GND.
      
 
      B(C). The hypothesis about the chassis floating was about possible mechanisms that would cause voltage transients getting coupled in to the long cable lines. It is possible if the chassis ground were dramatically different than the system ground, and then they were shorted that a large spike would capacitively couple, but that is not very likely.
      
 
      These failures feel more like an over voltage situation than an ESD failure.
      
 
      Is the ESD protection very close to the ADP5585, or is it on the other side of the cables? Closer to the part is the best location.
      
 
      RSchnell
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

      • 


    


Children
	
    No Data