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Can the AM26C31 take a 3.3V CMOS signal and convert it to a +/- 3.5V and +/-1.5V differential signal?

Jamaal_Charles
Genius 3245 points
Other Parts Discussed in Thread: AM26C31, AM26C32

 

Hi,

I need a Differential Driver and Receiver that will work with the following legacy signal:

Frequency: 60Hz

  Logic 1: +3.5V +-1.5V

  Logic 0: -3.5V +-1.5V

I need a Driver that will take a 3.3V logic (single ended) input and output the above legacy signal in differential form.  Likewise, I also need a differential receiver that will take this legacy signal and output a single ended 3.3V logic. I have been looking at the AM26C31 and AM26C32 but am unsure if they will meet my needs.  If not, do you know of another device that will do it?

Thanks!

  • 0
    TI__Expert 5175 points

    Greetings -

    Please clarify the questions more, as written it is confusing between single-ended and differential levels.

    It implies you have defined a single-ended system with a Logic 1 from +2V to +5V range and a Logic 0 to be from -2V to -5V.  This sounds like a single-ended system and is similar to RS232/423 or 562 type levels.

    However you call out differential, and note the 26C31.  This is a single supply device, and will gerenate  a VOD of >+2V for one state, and >-2V for the other, but actually  the signals are between GND and 5V.  Likewise there is a legacy device, the DS3691 (it is available but the datasheet reference is incorrect currently) - this is a differential driver that is powered from +5V and -5V, it will give a vary large VOD and also polar swing.  This might be a good fit for you.  It is a 5V device, you might need to level shift your 3.3V to 5V with a logic buffer if the VIH is not met.

    Geeting from your differential signals back to single ended is a bit easer, the DIFF REC usually have a threshold of +/-200mV for RS422 type RXs and can level shift back to the desired LVCMOS (3.3V parts are available).  Parts are available in many options of temp, supply voltage, package and other features. 

    See the RS422 tree for details.

    John Goldie

    DPS APPS / SVA

     

  • 0
    TI__Mastermind 28265 points

    Well Eric,

    I don't know whether this is what you want, but I can tell you what the AM26C31 does when you toggle input A between 3.3V and 0V.

    When input A is at 3.3V, the non-inverting output Y assumes 3.4V and the inverting output Z assumes 0.2V with both voltages being referenced to ground !  The differential output voltage, being defined as Vod = Vy - Vz is therefore +3.2V.

    When input A is at 0, the non-inverting output Y assumes 0.2V and the inverting output Z assumes 3.4V with both voltages being referenced to ground !  The differential output voltage is now -3.2V.

    Below is a nice little picture that clarifies the behavior of the driver. Interpreting your given output levels above would indicate a minmum positive Vod of +2V and a maximum positive Vod of +5V as well as a minimum negative Vod of -2V and a maximum negative Vod of -5V. If my assumptions are corrcet then these are the RS422-levels for a 100W load for no load.

    Is this what you meant ?         Regards, Thomas

  • 0 in reply to Thomas Kugelstadt
    TI__Mastermind 28265 points

    Sorry, the last sentence should read: ......then these are the RS422-levels for a 100W load (+/-2V) and for a no-load condition (+/-5V).

    - Thomas