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LMH0384 SDI input voltage levels

Goksan Eral
Prodigy 10 points
Other Parts Discussed in Thread: LMH0384

Hi,

We are using LMH0384 cable equalizer and we want to implement a lightning  protection circuit in front of the typical application circuit given in the datasheet.

However, I am confused by absolute input voltage levels. Our SDI input is in SMPTE 292M standard in which the voltage levels are given as 800mVp-p with 0 V offset. However, in datasheet, absolute maximum input ratings are given as -0.3v, Vcc+0.3v. Hence, the signal level in HD-SDI standard may reach -400mV and  lower than -0.3V in case of using AC coupling at the input pins and assuming 0 m cable length (If two 75ohm resistors are voltage dividers, the input will be -200mV and and it is still very close to -0.3V). Could you please explain where I am wrong?

Also, what can be the optimum voltage levels for the purpose of selection TVS diodes at the SDI input pins?

Thanks for your help.

  • 0
    TI__Mastermind 20820 points

    Hi Goksan,

    Somebody is looking into this and will respond shortly.

    Regards,

    Michael Peffers

    High Speed Interface Applications

  • 0 in reply to Michael Peffers
    TI__Guru* 88835 points

    Greetings,

    Absolute maximum rating on any input as you indicated is -0.3V to Vcc+0.3V. This is the allowed voltage range before the device gets damaged. It is not implied that we can operate the device under this condition for a long length of time though.

    LMH0384 Equalizer complies with SMPTE292 requirements. Please note data sheet input voltage swing in the DC Electrical Characteristic table(720mV min and 950mV max). For the equalizer to meet the data sheet cable reaches, the launch amplitude or the input voltage swing on either the SDI+ or SDI- pins has to be within 800mV +/- 10%(720mV to 880mV). This is the same spec or requirement that SMPTE292 calls for as well. This is a single ended AC voltage with minimum 720mV and maximum 880mV peak to peak swing.

    Please note ESD protection device may have high parasitic and thus may cause SMPTE return loss requirement violation.

    Regards,,,nasser