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  • TI Thinks Resolved

OPA2209: there is voltage on IN+ and IN- pin when input signal is floating, why?

Intellectual 2260 points

Replies: 4

Views: 221

Part Number: OPA2209

Hi 

OPA2209AIDGKR is used.

customer's circuit is as below,  which is used to sample LLC output 12V power rail current.

the power for OPA2209 is 12V comes from auxiliary power.

when AC power is plug in, auxiliary power flyback works, so 12V for OPA2209 VCC comes out, at this time, LLC is still kept turning off.

12V_Current is connected to DSP ADC pin.

in this condition, customer can see 0.6V at Pin5 and Pin6 of OPA2209, and +12V and +12VX is 0.3V.

after removing R282 and R283, customer can see 1V at Pin5 and Pin6 of OPA2209.

customer want to know why this is no input signal, but input pin has voltage?

thanks.

  • when LLC turns off, +12V and +12VX should be 0V.
  • In reply to Max Han:

    Hi Max,

    you violate the common mode input voltage range of OPA2209. See section 6.7 of datasheet.

    Kai
  • Marek Lis, MGTS
    Sr Application Engineer
    Precision Analog - TI Tucson

  • In reply to Marek Lis:

    Max

    I have not heard back from you so I will close this thread. Please reply if further discussion is needed.

    Thanks
    Dennis

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