LM6172: LM6172 problem of current from inverting pin

Eren Erdogan

Part Number: LM6172

Hi all,

In the following circuit, when enable input is float, i see 700mV dc voltage at inverting input of opamp. Thus, there is 70uA current from inverting pin of the opamp. However, LM6172 datasheet states that max bias current is 4uA and max offset current is 3 uA. What is the reason of this current? Is this normal?

Best Regards,

Eren

over 7 years ago

0 kai klaas69 over 7 years ago

Guru 140200 points

Hi Eren,

the input bias current specification is only valid for an OPAmp with a normal working feedback loop. A normal working feedback loop means that the output is able to make the voltage difference between the + input and - input minimal. But in your scheme there's no such intact feedback loop. Quite the contrary, you force a large differential voltage between the inputs. Then, a much higher input bias current might flow.

Kai

0 Eren Erdogan over 7 years ago in reply to kai klaas69

Intellectual 280 points

Thanks Kai

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LM6172: LM6172 problem of current from inverting pin