• TI Thinks Resolved

SN74AHC4066: Switch fails under some conditions

Prodigy 20 points

Replies: 3

Views: 65

Part Number: SN74AHC4066

We use SN74AHC4066 ( QFN − RGY) in our product to switch signals between camera and lens. Power supply from camera is 5V, signal levels are normally in 0 - 5V range.

The problem is that appx. 1 in 30 our products fails with end users (while successfully tested on several cameras before sending)  and according to our tests it's SN74AHC4066 which starts to behave strange.

We suspect that it happens when camera is turned off and signal levels becomes appx 1V higher than power supply. (VCC = 0, signal = 1V). But we are not able to reproduce this situation in controlled environment, it happens randomly with camera and lens only. It means, if we apply 1V to signal line with Vcc = 0, it does not break the switch.

Usually our product stops working, then after a day or two it is back to normal. In rare cases we can "break" our product by removing battery from camera, and then "fix" the product by  turning it on and off several times.

Another example: normally voltage drop (measured with multimiter in diod mode) between signal line and 0 is 1.6V. But "broken" switch has only 0.1V. When we heated the switch to 100 C, the voltage drop returns to 1.6V and our product starts to work correctly.

We also once registered 0.02V voltage drop between signal lines.

The strange thing is that most our products "fix" themselves while traveling back from our customers to us.

That is very frustrating and your help would be very much appreciated.

  • Danylo,

    Is this use case you described "(VCC = 0, signal = 1V)" for the SN74AHC4066 a normal condition? If so, that's probably your problem there. This device doesn't have powered off protection. Meaning that when the device is powered off it isn't protected from input signals and we can't promise the same functionality as the datasheet states when the devices have been used in a manner that exceeds what is recommended. Could you possibly alter the power sequencing so that the device is powered on before you see those errant signals on the data lines?
    My guess is that the devices are damaged but not quite 'broken' so your seeing strange behavior when you test them. For example, when the temperature is raised you may be lowering the Vth of the FET so the signal can pass through. But at lower temperatures you aren't breaking the threshold. Since the devices are damaged though we can't guarantee this to be the actual problem, but it's my best guess from the information presented. 

    If power sequencing can't be changed, you'll want to find a 4channel SPST that has powered off protection. The TMUX1511 may be a better replacement. It will offer the powered off protection to help in this power sequencing scenario and comes in UQFN package as well. 

    Rami

  • In reply to Rami Mooti1:

    Many thanks for the suggestion. We ordered TMUX1511  and time will tell if it helps. So far we are not able to "break" SN74AHC4066 with Vcc = 0 and signals up to 5V/0.5A, so there might be other reasons for such behavior.

  • In reply to Danylo Kozub:

    Danylo,

    I hope this works our for you!
    One quick note though, I'm not sure if you're saying that the 5V/0.5A condition is just the max level you use to actually attempt to 'break' the chip but if these are your normal signals, both the TMUX1511 and SN74AHC4066 don't support a current that high and we can't guarantee any performance past what the datasheet states.

    Rami