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In this App note, page 7, example 3, can someone tell me from where the values for IBN and IBI are coming from? I.e.

enter image description here

\$I_{BN}\$ = -(5 nA + 0.5 nA)
\$I_{BI}\$ = (5 nA - 0.5 nA)

I'm using this MCP601 Op-amp

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  • I think the 5 nA is the input bias current and the 0.5 nA is the input offset current. Offset current is the difference between bias currents for the two inputs. But I can't tell you what circuit uses the 1k8 resistor. Nor can I tell you if those currents are for an MCP601 (they don't appear to be). Why don't you ask what you are trying to calculate . – Andy aka Mar 16 '23 at 18:55
  • The app note says they are using the MCP601 as an example, and I can see the 5nA but not the 500pA. Maybe its an estimate. Maybe they got it from an earlier version of the datasheet. It appears to be the input offset current, which is not specified in worst-case terms. – Spehro Pefhany Mar 16 '23 at 19:38

2 Answers2

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Ibn and Ibi are input bias current currents. They result in the small current that leaks into the high impedance terminals of the opamp (have to have some resistance for the amplifiers of the opamp to measure the signal, they designers try to make the resistance as high as possible for the application).

For the MCP601 they are found here, and vary with temperature.

enter image description here Source: MCP601 datasheet

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  • can you tell me from where the values for IBN and IBI are coming from?IBN = -(5 nA + 0.5 nA) IBI = (5 nA - 0.5 nA) –  Mar 16 '23 at 19:02
  • They are inherent to the operation of the input stage of the opamp. Some small current has to move into or out of the input pins of the transistors will not function. The values are on the datasheet. The values in the app note are typical, not related to any specific part number. – AnalogKid Mar 16 '23 at 19:37
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where the values for IBN and IBI are coming from? I.e.

IBN = -(5 nA + 0.5 nA)

IBI = (5 nA - 0.5 nA)

They are inherent to the operation of the input stage of the opamp. Some small current has to move into or out of the input pins or the transistors will not function. For the part number you mention, the values are on the datasheet as shown in another answer. The values in the app note are typical, not related to any specific part number.

AnalogKid
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