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LMH0387 Launch amplitude Fine Control Resister(02h, 6:3)

Toshi
Expert 1780 points

Other Parts Discussed in Thread: LMH0387, LMH0384

I'd like to confirm the description of Launch amplitude fine Control resisters(02h, 6:3). On the LMH0387 datasheet(REVICED April 2013); Almost all settings of gain are +20% higher than LM0384's settings. Are there correct ? (Did you set the base gain of LMH0387 higher ?)
  • 0
    TI__Expert 4400 points

    The base gain of the LMH0387 is actually lower by default, which is why it must be manually configured to the optimal setting via the SPI after device power up (LMH0387 register 0x02 bits 6:3 must be changed from 0000 to 0110 for typical applications, which adjusts the gain +20% higher to match the LMH0384 and similar SDI cable equalizers).  Once this adjustment is made via the SPI, the gain is the same between the LMH0387 and LMH0384 equalizers.

    Gary Melchior

  • 0 in reply to Gary Melchior
    Expert 1780 points
    Gary, thak you for your reply. I see, the gain of LMH0387 is lower than LMH0384's. Well, I'd like to confirm the following condition. If a driver amplitude is 640mV(-20%), a resister setting of LMH0384 should be "0110" : -20% from nominal. Under ths condition, LMH0387 cannnt optimise amplitude ? or it can optimise the amplitude under the following setting? 0x02 bit 7 ..............."1" Optimized for 6 dB external attenuation 0x02 bits 6:3 ..........."1111" : +60% from nominal. 640mV(+6dB and Optimise +60% from nominal) ===> 800mV Is my understanding correct ?
  • 0 in reply to Toshi
    TI__Expert 4400 points

    Your understanding is correct.

    Gary Melchior

  • 0 in reply to Gary Melchior
    Expert 1780 points
    Gary, thank you very much for your help. I understood the resister and the function.