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LMH0318: OUT0 amplitude too small by default, OUT0_VOD register not as expected.

user6452651
Prodigy 50 points
Part Number: LMH0318

Tool/software:

I get only 700 mV of amplitude on OUT0 instead of 800 mV as expected.

When reading the OUT0_VOD register (0x80) I get 0x20 instead of the default value 0x54.

0x20 is not an expected value because this is an invalid value for bit 7-4 and the reserved bit 2 is not set.

By modifying this value, I get also 700 mV with the 0x54 value. I must set 0x50 to get the expected 800 mV of amplitude.

What is wrong ? Why I didn't get the 800 mV by default? Must the bit 2 be set or clear. Which value should I set to this register?

Regards

Jean-François

  • 0
    TI__Guru* 91400 points

    Greetings,

    Yes bit 1 must be set so you can control VOD through register. Each step is about 6mv.

    Regards, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 50 points

    Hello Nasser,

    I'm talking about the bit 2 (reserved should be set to 1)... Is the datasheet not up to date? do you have an update of the description of this register ?

    I tried several values, I got the following values:

    OUT0_VOD reg (0x80)     measured SDI ampl. [mV]
    0x20                                    721
    0x24                                    721
    0x30                                    765
    0x34                                    634
    0x40                                    791
    0x44                                    681
    0x50                                    833
    0x54                                    721
    0x60                                    873
    0x64                                    765
    0x70                                    922
    0x74                                    793

    Step is not 6 mV and the logic is not trivial.

    0x50 seems to set an adequate value.

    Is 0x50 an allowed value even if bit 2 is not set ?

    Regards

    Jean-François

  • +1 in reply to user6452651
    TI__Guru* 91400 points

    Hi Jean-François,

    Yes 0x50 is allowed and valid. Suggestion is to check other data rates VOD as well since this may affect other data rates.

    Regards, Nasser