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CD40109B enable pin drive current and failure

Jing Xie
Prodigy 20 points
Other Parts Discussed in Thread: CD40109B

Hi, We are using CD40109B for our same production boards for over 20 years. The IC is enabled at pin2,7,9,15 by 12VDC through (4.7kohm + 15kohm) serial resistors. VDD is at 15VDC. Recently we saw quite often that the voltage at CD40109B enable pin (2,7,9,15) dropped to 0 ~ 3V, while the driving voltage from the system bus is still remaining at 12VDC. I either have to replace the IC or decrease the current limit resistor value from 15kohm to 6kohm with jumper wires, resistor pot. The system is at room temperature testing cage. It runs the final test for a few weeks, and then suddenly a lot of boards failed near at the same time.

I would like to know how much current needed to enable CD40109B under normal condition. According to my understanding from the data sheet, it is in ~ 1uA range for each IC. Our system bus can provide up to 2.6mA driving 10 same kinds of boards at the same time. What could cause the failure of CD40109B? How can I prevent the damage happened again? Should I change the design how we enable this IC?

Thank you! Jing 


 
  
  
  
  
  
  
  
  
  
  
  
  
 
 
 


  • 0
    TI__Expert 6335 points
    Jing,

    Thank you for your patience. I've assigned this to the appropriate apps engineer. They will get back to you shortly.

    Best Regards,
    Nirav
  • 0
    TI__Guru 55970 points
    Hi Jing ,

    want to understand why do you have a series resistor of 16kohm before the enable pin ? The enable pins are supposed to be high impedance pins with little current consumption . so with smaller resistor , you should be able to drive the boards . What is the drop across the resistor and total current consumed on that per device ? what would the good board read at the enable pin vs the bad board ?
  • 0 in reply to Nirav Patel
    Prodigy 20 points
    Hi ShreyasRao, Thank you for your reply! The enable pin normally uses very small amount of current. No need to put large resistor in series there. But the board has a lot of relay switches, also shared the power supplies, control signal bus with other similar boards together (up to 10 boards). According to the recommendation for CMOS CD4000B series latch up (A lot of them on line), the design prefers to add a large value resistor (10kohm up to 100kohm) to prevent the spikes generating too much current to the gate, and latch up or even damage the IC. If it is possible, I would like to share some of our schematics with you in private communication. Under normal condition, there is almost no voltage drop across the resistor. For bad cases, the voltage drop could be (12VDC -12VDC ~ 0V) to (12VDC - 3VDC ~ 9V) or (12VDC - 1VDC ~ 11V). Sometimes, the voltage drop always there even I removed CD40109B. The problem does not happen all the time. Only after certain testing time. It is intermittent. Sometime it recovers after the power recycling. Sometimes, it got permanent damage. Remember our production is 20 year old. Only in recent a few month, the problem happens quite often. No design, manufacture changes. We need to find the way to prevent the problem happening again.
  • 0 in reply to Jing Xie
    TI__Guru 55970 points
    Hi Jing ,

    You can send the schematics to me in the private message to have a look at it . any scope shot and plots of the input voltage / Vcc / gnd can also help .
    Do you think there were any ESD events which could potentially damage the devices during handling and manufacturing or assembly ? do you have the lot numbers on the device which we can also help to see if there was anything we would notice ?