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ISO3086 VOA/VOB

ttd
Mastermind 7980 points
Other Parts Discussed in Thread: ISO3086

Dear Technical Support Team,

I have a question about ISO3086.
Do you have a specification of VOA/VOB?
I'd like to know about it, but I can't find it on datasheet.
I think that I can calculate the spec from VOD and VOC.

Is following calculation correct?
I refer to "Figure 12. Test Circuit and Waveform Definitions For The Driver Common-Mode Output Voltage".

<Calculation for VOA / VOB>

■MIN
VOA = 1V+0.75V = 1.75V
VOB = 1V-1.15V = -0.15V

■TYP
VOA = 2.6V+1.15V = 3.75V
VOB = 2.6V-1.15V = 1.45V

■MAX
VOA = 3V+1.15V = 4.15V
VOB = 3V-0.75V = 2.25V

＜datasheet spec＞
|VOD|: MIN 1.5V / TYP 2.3V(RL=54Ω)
VOC: MIN 1V / TYP 2.6V / MAX 3V

www.ti.com/.../slos581g.pdf

Best Regards,
y.i

  • 0
    TI__Intellectual 1815 points

    y.i.

    This is a good approximation of what you will see. The only caveat is that min of Voc and Min of Vod need not occur simultaneously.

     May I ask why do you need this VOA/VOB separately, RS485 bus is fully defined by VOC and VOD.

    Regards,

    Sarangan Valavan

  • 0 in reply to SaranganValavan
    Mastermind 7980 points

    Hi Sarangan,

    Thank you for your advice.
    I understand that min of Voc and Min of Vod need not occur simultaneously.
    Following are fixed version. Could you check it?
    Customer'd like to add earth fault detection for RS485, so they'd like to know exact ranges of VOA/VOB.

    ■MIN
    VOA = 1V+0.75V = 1.75V 　←　VOC MIN 1V / VOD MIN 1.5V ⇒NG: It doesn't occur simultaneously

    VOA = 1V+1.15V = 2.15V 　←　VOC MIN 1V / VOD TYP 2.3V
    VOB = 1V-1.15V = -0.15V　←　VOC MIN 1V / VOD TYP 2.3V

    ■TYP
    VOA = 2.6V+1.15V = 3.75V ←　VOC TYP 2.6V / VOD TYP 2.3V
    VOB = 2.6V-1.15V = 1.45V ←　VOC TYP 2.6V / VOD TYP 2.3V

    ■MAX
    VOA = 3V+1.15V = 4.15V ←　VOC MAX 3V / VOD TYP 2.3V
    VOB = 3V-0.75V = 2.25V ←　VOC MAX 3V / VOD MIN 1.5V

    ＜datasheet spec＞
    |VOD|: MIN 1.5V / TYP 2.3V(RL=54Ω)
    VOC: MIN 1V / TYP 2.6V / MAX 3V

    Best Regards,
    y.i