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LMH6525: Question on oscillation signal

Joyce Gao
Intellectual 2030 points
Part Number: LMH6525
Other Parts Discussed in Thread: LMH6526

Hi expert,

I have 2 questions for LMH6525:

1. What is the relationship between the input differential lvds signal and the oscillation signal? The datasheet states that lvds controls the on and off of the oscillation signal, and the timing diagram only shows the control of the on and off of the current.

2. Will the oscillation occur once the oscillation signal is enabled?

Many thanks!

Joyce

  • 0
    TI__Intellectual 2030 points

    Hi expert,

    Generally, I would like to know the use case of LVDS input, in what cases it is needed to control LMH6525?

    Thanks!

    Joyce

  • 0 in reply to Joyce Gao
    TI__Intellectual 2030 points

    Hi expert,

    I have gone through the datasheet and I think I figured out the answer. LMH6525 uses LVDS for OSC control, OSC switches under high frequency so need LVDS. LMH6525 and LMH6526 both use LVDS for output channel control, due to high frequency, also LVDS needed. So LVDS signal is used both for OSC enable and channel selection.

    Still 1 confusion from my side: Why use LVDS also for OSC enable? Couldn't keep it on? Is it for power saving?

    Correct me if any wrong understanding, thanks!

    Joyce

  • 0 in reply to Joyce Gao
    TI__Expert 6050 points

    Hi Joyce,

    Please see this note in the Layout section under the Inputs subsection of the datasheet

    The oscillator is enabled and disabled in order to control when the output current is modulated. It is good practice to only enable the oscillator in combination with the write pulse.

    LVDS signaling is used to enable or disable Channel 2, 3, and 4. LVDS signaling is needed in ordered to operate the channel control at the high speeds.

    If you would not like to use LVDS signaling for the oscillator control, the LMH6526 has oscillator control using a TTL/CMOS signal.

    Thanks,

    Nick

  • 0 in reply to Nick Nauman
    TI__Intellectual 2030 points

    Hi Nick,

    My question is why use LVDS also for OSC enable? Couldn't keep the OSC on? What's the benefit for switching on and off instead of keeping OSC on? Is it for power saving?

    Joyce

  • +1 in reply to Joyce Gao
    TI__Expert 6050 points

    Hi Joyce,

    You are able to keep the OSC enabled and switching is not required. The OSC will add both an amplitude and a frequency to the output current so keep that it mind. Switching is used for if you want to disable the modulation of the output current. 

    Thanks,

    Nick

  • 0 in reply to Nick Nauman
    TI__Intellectual 2030 points

    Thank you Nick!

  • 0 in reply to Joyce Gao
    TI__Expert 6050 points

    Hi Joyce, 

    Glad I could help. Please feel free to reach out if you have any further questions.

    Thanks,

    Nick