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SN74HC4060: SN74HC4060 Design Risk Accessment

Part Number: SN74HC4060

Hi Team, 

My customer is design the system with SN74HC4060 for the watchdog function as below. 

Usually either R7A (1Kohm) or R9A (1Kohm) is connected to get the output.

However, in some case, they made a mistake, that connected both R7A, and R9A together. then it leads to the RST has the high output by mistake, even with the normal feeding operation. You can check the waveform as below. the blue line is the SN74HC4060's PIN12 waveform, while red line is the power rst output. 

And it was found out if connecting the two resistors together, the issue can be reproduced 100%.

so the questions is that, if connected both R7A AND R9A together, is there any possibility to lead physical damage on the SN74HC4060 device?

  • When Q13 and Q14 output different values, there will be 5 V over 2 kΩ, which results in 2.5 mA. This is perfectly fine.

  • Hey Steven,

    As Clemens has stated, since you have 2k ohm with both resistors in series even in worst case scenario where one output drives high and the other low, there won't be enough current to damage the device. However, the slow looking transition rate of the CLR pin is what concerns me here. I can't really make out what the time division is on the scope shot so I'm not 100% sure, but it looks to be really slow.

  • Thanks Clemens for the quick response!

  • Thanks Dylan for the comment, especially for the suspicious CLR actions. 

    Honestly, we do find the Dv/Dt is out of spec for the CLR pin, but according to multiple tests, it turned out that, even with the same input of CLR,  it could work well with single resistor connection as the output.

    For the issue cases, when connecting both resistor, it could work well for a while, which can be checked in below image for the use case, refer to the first 2 wave CLR PIN got. 

    If this part is suspicious, it means all those boards that customer designs had the same risk. Is that right?

    I would appreciate your comment on this! Many thanks!

  • Hi Steven,

    I don't see what it is hooked up to the clear pin, but most likely each board will have a slow transition regardless if two resistors were populated or not.