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SN74LVC1G3157: SN74LVC1G3157 Switching Failure

Yazhu Liu
Intellectual 1410 points
Part Number: SN74LVC1G3157
Other Parts Discussed in Thread: TS5A12301E, TS5A22362

Using for video signal switching.

When the analog switch is switched from pin 3 to 1, a voltage of 3.3+Video appears at pin 3, and because of this voltage, Vout cannot switch back to pin 3.

 We find a surge voltage(because of Integrated inductance) at Vcc when the switching happened. And the datasheet of SN74LVC1G3157 recommends waiting until VCC has ramped to a level in Recommended Operating Conditions before applying any signals, so we suspect that if this surge voltage of Vcc cause the problem.

So will the unstable of Vcc causes the switching failure? If not, then is there any other probability may cause the problem?

Sincerely thanks for your help!

  • 0
    TI__Mastermind 45340 points

    Yazhu,

    You are correct that this device doesn't have powered off protection like the TS5A12301E and Vcc must be within the recommended operating conditions before signals are placed on the I/O path.  

    A typical symptom of signals on the I/O path before Vcc is high leakage into the device I/O pins to ground or Vcc through the ESD protection once it is above the forward bias voltage ~0.5V.

    I would like to understand a little bit more about "switching failure" means.

    Do you have a scope capture of the pin 1, pin 3, pin 5, and pin 6 during both cases?

    Do you suspect the device is damaged?  Does replacing the device with a new IC allow normal switching? 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Intellectual 1410 points
    Thank you so much Adam.

    For more information, the "switching failure" means that when the switching is switched from pin 3 to pin 1, it works well, but when we switch it back from pin 1 to pin 3, it fails, and we can detect a VCC + Video voltage signal from pin 3. And once we short pin 3 to ground to release the voltage signal, we can switch from pin 1 back to pin 3 again.

    We've tried the replacement with a new IC, but the problem is still there.

    According to your information, we suspect that may because the minimum AC input voltage is less than -0.5V that cause this failure. I've asked our customers to test the device again to get the scope capture of the pin 1, pin 3, pin 5, and pin 6 during the cases, as far as I get the result, I'll show it to you.

    Thanks again!
  • 0 in reply to Adam Torma
    TI__Intellectual 1410 points
    Hi Adam,

    Sorry for disturbing you again. But our team really need some help from you.

    Actually our customer are using SN74LVC1G3157 for AC video signal switching, whose minimum value is about -1V, lower than VI/O minimum value -0.5V of SN74LVC1G3157, which may cause the switch failure. So they would like us to introduce pin-to-pin device which can match their requirement. So could you give me some advice on that?

    Thank you so much.

    Yazhu
  • 0 in reply to Yazhu Liu
    TI__Mastermind 45340 points
    Yazhu,

    Most signal single supply switches only support voltages down to 0V. What is the type of video signal are you using that is down to -1.5 V? Do you know what video driver they are using?

    There is an audio switch TS5A22362 that will accept -1.5 V signal but doesn't have a high bandwidth.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Intellectual 1410 points
    Hi Adam,

    Thank you so much.

    Checked with our customer, the video signal is of CVBS type. And they output the video signal directly without a video driver.

    Thanks again,
    Yazhu Liu
  • 0 in reply to Yazhu Liu
    TI__Mastermind 45340 points

    Yazhu,

    I'm not familiar with the CVBS video signal.  Would you please provide the voltage range and bandwidth of the signal you are attempting to support?  This will help make sure the switch will support your signal. 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Intellectual 1410 points

    Adam,

    Sorry for answering so late, I've got serious personal things to deal with and forgot to check E2E. Really sorry again.

    The voltage range of the signal is between -1V to 1V, and its bandwidth is 6MHz.
    Our customer would like us to find pin-to-pin device for them so that they won't have to change the design. But as far as we know, there do not seem to have pin-to-pin device which can support their requirements. I've already update your solution TS5A22362 to them, and haven't got their feedback yet.
    I'm the FAE Intern of Suzhou branch, TI China. Really thank you for the help.

    Thanks again.
    Yazhu

  • 0 in reply to Yazhu Liu
    TI__Mastermind 45340 points
    Yazhu,

    You are correct we don't have a p2p solution today to support -1V to 1V signals with a single ended supply. I will bring this information up to our product definition team to see if they would like to develop such a switch.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Intellectual 1410 points
    Adam,

    Thank you so much. Please update the information to me after you get it.

    Thanks again.
    Yazhu Liu
  • 0 in reply to Yazhu Liu
    TI__Mastermind 45340 points
    Yazhu,

    The product definition and development cycles are long and proprietary. I will not be able to provide additional information at this time.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Intellectual 1410 points
    Adam,

    Sure, got it.
    Thank you so much for your help.

    Yazhu