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CD4047B: the unique operation of the monostable multivibrator and retrigger randomness

user6473012
Prodigy 50 points
Part Number: CD4047B
Hi,
I'm trying to run the chip using the cd4047 chip in monostable mode with time extension on demand. The designed time tM = 2.48 RtCt is approx. 38 sec. (ceramic 30uF and 510kOhm). 12V power supply filtered with 100uF / 25V capacitor. I made the test on 2 copies - the same problem occured. I am sending an oscillogram of signals on individual pins of the system.
I am asking for help in finding the cause. Please provide more detailed information about the operation of the system and design recommendations. Best regards
  • 0
    TI__Mastermind 44640 points

    Hi,

    The data sheet has all the info needed to set up this device. First thing I recommend is to check all of the control signals to make sure they are at the right levels. Then I would check to make sure you are meeting the timing requirements in the Dynamic Electrical Characteristics.

    It would help to see a time scale for the scope shot. It would be good to also zoom in around the pulse giving issues.

  • 0 in reply to Dylan Hubbard
    Prodigy 50 points

    Thanks for quick replay. The time base is visible on the picture - 25.0 sek/div. Driving signals are beeing delivered from outputs of standard cmos circuit (cd4093)

  • 0 in reply to user6473012
    TI__Mastermind 44640 points

    Hi,

    Thanks for those details, were you able to perform all of the other checks I recommended?

    Also, are pins 8 and 12 tied together? 

  • 0 in reply to Dylan Hubbard
    Prodigy 50 points

    Hi, As You can see on the oscillogram: pins 8 and 12 are marked as tied together, and they are tied indeed. The problem is that retrigger execution is randomness. I really don't know if it is possible to execute it any state of the system, what happens if i give multiple retrigger pulses one after the other while timing  (datasheet does not mention about that!). The other problem is that I noticed about twice for a long time (see oscillogram - changes in the state of oscillator output). Why the system does not guarantee repeatability of operation?

  • 0 in reply to user6473012
    Prodigy 50 points

    Hi, again.

    In addition to my thoughts - Fig.8 Retrigger mode waveforms, from 4047 datasheet.

  • 0 in reply to user6473012
    TI__Mastermind 44640 points

    Hi,

    You basically recreated the example to the right of that waveform and in that scenario the retriggering should be happening. Unfortunately, due to the age and it being a part acquired by Harris, support for this part will be limited. I still recommend zooming in on the pulse that is being ignored to see in a smaller time scale if anything is visible. 

  • 0 in reply to user6473012
    Prodigy 50 points

    Hi,

    my example of pulse no 2 is not exactly like the one on the right - I was trying to explain my doubt about the situation when the retriggering pulse is comming during the change of oscillator output level. I am constantly investigating whether the retrigger pulse can come at any point in the system state because of retrigger randomness. At the moment I am abandoning this project with cd4047 and redesigning it with a different chip. Thank you for your comments.

    

    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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