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LMH7220: LMH7720 configuration using hysteresis

na na78
Guru 16770 points
Part Number: LMH7220

Hi

Our customer is considering the following system configurations.

1. The output of differential amp is connected to LMH7220 with using hysteresis.

  

2.  DAC output is used for changing reference.

Could you please check them?

And if they are offering issues please point it out.

BestRegards

  • 0
    TI__Guru 60786 points

    Hello Na Na,

    Please provide the resistor and capacitor values and expected threshold values. What is your supply voltage?

    I'm not sure that the DAC output will achieve the expected results.

    Since the input signal is AC coupled, the DC "reference" will be set by the common mode of the output (~1.2V) through the feedback resistors. Tugging on one side will distort the waveform (no longer symmetrical) and hysteresis.

    Are they trying to adjust the center point or widen the thresholds?

  • 0 in reply to Paul Grohe
    Guru 16770 points
    Hi Paul

    Thank you for your reply.

    I'll check purpose of using such a configuration.

    I have question about the usecase of ① that I attached.

    According to the datasheet, LMH7220 is used for Fast Differential Line Receiver application.
    In this case, is the configuration of LMH7220 with use of hysteresis like ① ?
    Because the Figure 28 shows the configuration with a single output to the positive input.
    (Maybe, positive out to positive input feedback)

    From Negative Out to Negative Input configuration for use of hysteresis, acceptable?

    BestRegards
  • 0 in reply to na na78
    Guru 16770 points
    Hi

    I appreciate if you could reply.

    Bestregards
  • 0
    TI__Expert 3350 points
    Hello na na,

    Paul Grohe in his last posting provided you feedback about your questions with as much information he had about the circuit. Please provide the needed additional information he requested in the posting to determine if the part would function properly in the shown configuration.

    Thanks,
  • 0 in reply to Bahram Mirshab
    Guru 16770 points

    Hi Bahram

    Thank you for reply and I'm sorry for being ambiguous question.

    Please forget about DAC and AC coupled input.

    I attached new image.

    I didn't set capacitor and resistor value.

    I want to confirm if the configuration of hysteresis for differential inputs is correct with the connection above.

    BestRegards

  • 0 in reply to na na78
    TI__Expert 3350 points

    Hello na na,

    The configuration shown in your posting is described in TI application note SNOA478A “AN-1534 Demo Board LMH7220 High Speed LVDS Comparator (Rev. A) “ at the link www.ti.com/.../technicaldocuments. The schematic is shown in Figure 1 on page 3. Section 2.1 and 2.2 describe the circuits. Section 3 provides layout consideration.

     

    Best regards,