ADG3304 Level Translator not working

Hello,

I have just implemented an ADG3304 level translator into a new design and it is not functioning as expected. I am hoping others have had experience with this particular IC and can point me into a direction that yeilds the correct results.

I am using the ADG3304 to connect an MCU operating at 3.3V to drive a TTL signal operating at 5.0V.  The problem that I am experiencing is that when the A side goes to logic low (0V), the Y side goes to 2.5V instead of zero volts.  I have attempted to connect a pull down resister to the Y output to see if this would allow the signal to go to zero volts, however, it does not.  When the A side goes to logic high, the output also goes to logic high (5V) as expected.  The issue is when it goes to logic low.  Since TTL devices have a on threshold of about 1.2V, this 2.5 volts output is creating a huge problem for me.

Thanks,

James

  • 0
    •  Analog Employees 
    on Nov 3, 2014 9:58 PM

    Hi James,

    Could you please provide a schematic of your setup?

    Regards,

    Stephen

  • The CAM1_Trigger is coming directly from a Microchip
    Technologies pic24EP512GU810 micro controller.  The output is attached to
    a TTL device at the other end in a downstream device.  When I was taking
    the measurements, I am taking it with and without a connection to TB1.  I
    have tried to use a pull down resister at TB1 pin 1 and pin 2 as well.
    The problem still remains, U3 will drive the outputs to +5.0 but it will not
    drive it to 0 volts.  I have even tried to put a diode in line with a pull
    down resister as still I get the same situation.

     

    I my particular application, it would have been better to just
    have a quad unidirectional level translator, but it seems difficult to find
    unidirectional level translators.  They are all auto direction
    sense.  What is the proper way to utilize there IC’s?

     

    Thanks,

     

    James


  • 0
    •  Analog Employees 
    on Nov 12, 2014 2:51 PM

    Hi James,

    Because the load is TTL is the reason why the device won't drive logic low (0V). A TTL logic low requires a large current draw of around 1.6mA which the device is not able to provide as the ADG3304 is designed to drive CMOS compatiable loads.

    A recommendation to solve this problem would be to add CMOS buffers between the outputs of the ADG3304 and the load. This would mean that the part would only be able to operate in the one direction but as you said your application only requires unidirectional capability then this could be a possible solution for you.

    Regards,

    Stephen

  • Thanks for the info.

    I have been looking around for CMOS to TTL buffers, however it seems that none exist.  They have TTL to CMOS available, but not the other way around.  It is sad really because it seems that TTL at 5.0V has been lost in the general electrical community, however TTL interfacing is an extremely strong driving force in the industrial equipment industry.  I think my only recourse is to use an open drain CMOS buffer to achieve a higher current drive/interface to my TTL controlled device.  I just hope I don't loose much bandwidth for this.

    Regards,

    James