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# MAX41400 unlisted input impedance (unknown)

Category: Datasheet/Specs
Product Number: MAX41400

What is the MAX41400 input impedance for differential and common? I don't believe it's listed but its a very important parameter for my uses

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• Thank you for reaching out and sharing your inquiries with the team.

Regarding the CM and Differential Input impedance of MAX41400, no data is available on the datasheet EC spec table.

Though…

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• Hi

Thank you for reaching out and sharing your inquiries with the team.

Regarding the CM and Differential Input impedance of MAX41400, no data is available on the datasheet EC spec table.

Though navigating with the TPC plots, we can use useful information on page 9 (toc05) to estimate the input impedance. https://www.analog.com/media/en/technical-documentation/data-sheets/MAX41400.pdf

I can’t find any similar related plots for IB vs Differential -Voltage; we can look further, and my colleague will get back to you.

Utilizing the VDD = 3.6V information, as the graph has a linear portion.

We can use two points from the linear part of the graph: Point 1 and Point 2.

• Pt1; Vcm = 1V, IBias = -225pA
• Pt2; Vcm = 2V, IBias = -40pA

The ratio of Zcm = Delta VCM / Delta IBias:

Computing for Zcm = (2-1) / (-40pA + 225pA) = 5.4054Gohms

I hope this initial data will help you.

Regards,

• Thanks a lot Arsol! This may be sufficient actually. Also i used for differential Z this equation: Zdiff = (input offset voltage / input bias current) * max gain

Zdiff = (1uV / 10pA) * 200 V/V = 20MOhm. This actually seems to work for other amplifiers like AD8237 and the AD8235, where each of these metrics are available to confirm.

This may be a 'janky' method, but yours is sound haha.

Thanks!

Matt

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