LMH7220: LMH7220 input impedance

Bing -PSC Lu

Part Number: LMH7220
Other Parts Discussed in Thread: BUF602

Hi,

I am trying to figure out a buffer or comparator for my high speed sensing circuit.

The short propagation delay of LMH7220 seems pretty good for me. However, I'd like it has very low input capacitance so that it doesn't affect my signal.

Do you have the equivalent input capacitance of the part?

Thanks.

Bing

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Bing,

should be arround 2.5pF, according to page 20 and 21 of datasheet.

Kai

0 Jonathan Nguyen over 4 years ago

TI__Expert 4555 points

Hi Bing,

You can expect roughly 4-5pF of capacitance on the part.

Regards,
Jonny

0 Bing -PSC Lu over 4 years ago in reply to Jonathan Nguyen

TI__Intellectual 1585 points

Hi, Kai and Jonny,

Thanks a lot for the help. Unfortunately that capacitor is too large for my application. I am going to look for better ones.

Bing

0 kai klaas69 over 4 years ago in reply to Bing -PSC Lu

Guru 140200 points

Hi Bing,

what capacitance would be good for you?

Kai

0 Bing -PSC Lu over 4 years ago in reply to kai klaas69

TI__Intellectual 1585 points

Hi, Kai,
I am looking for something less than 2pF, but need to have very fast speed, basically higher than 100MHz or less than 5ns of delay time.
I need a buffer or comparator to do the job.
Thanks.
Bing

0 Jonathan Nguyen over 4 years ago in reply to Bing -PSC Lu

TI__Expert 4555 points

Bing,

Generally our comparators have roughly 2-3pF of input capacitance, however the package it comes in adds an extra 1-2pF.

What kind of application requires this high speed comparator with very low input capacitance?

Regards,
Jonny

0 Bing -PSC Lu over 4 years ago in reply to Jonathan Nguyen

TI__Intellectual 1585 points

Hi, Jonny,

I am working on a high speed sensing circuit that detects the switch node voltage. I really need a buffer to show me the exactly the waveform. Any capacitor on the input pin would slow down the sensing circuit and cause a distortion on the circuit.

I am looking for either a buffer or comparator, because eventually, the signal needs to be used on a comparator. But the accurate measurement on the waveform is most important for me.

I tried to use BUF602 and it seems work well. Its input capacitor is about 2pF.

Bing

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LMH7220: LMH7220 input impedance