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LMH6553 single ended operation

Grant Downie1
Prodigy 125 points
Other Parts Discussed in Thread: LMH6553

Dear Sir/Madam,

I am looking at using the LMH6553 to interface to an ADC because of the clamp feature.
The ADC input has 27K from each input to ground and 5.8pF from each input to ground.
The ADC common mode input is 2.0V and input min/max is 1.3V to 3.0V.

The LMH6553 would be connected single ended and driven from an VFB op amp.
I would like to use a 40MHz RC low pass filter between the

LMH6553 and the ADC. The application requires a flat frequency response (no peaking) for the pulse input.

The datasheet shows peaking with large load resistance. Does this seem possible?

Regards Grant

  • 0
    TI__Genius 13935 points
    Hello Grant,

    The LMH6553 would have a very peaked frequency response with a 5.8pF and 28k Ohm load. However, you can use external resistance to make the ADC easier to drive. If you place a differential 1000 Ohm resistor in front of the ADC and use series 40 Ohm resistors you can get the curve shown in Figure 10 of the amplifier datasheet.

    Since you want to use a filter between the amplifier and the ADC you can use the filter to help flatten the frequency response as well. Figure 63 shows one possible configuration. Keep in mind that filter losses may require a larger supply voltage if you want to drive the ADC to full scale.

    Regards,
    Loren
  • 0 in reply to Loren Siebert 1
    Prodigy 125 points

    Hi Loren,

    Thank you.

    Regards Grant