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LMC6042: huge sensitivity to electrostatic external field of a photodiode transimpedance circuit based on lmc6042

bernard genot
Intellectual 560 points
Part Number: LMC6042

I am using a lmc6042 in a transimpedance circuit that amplifies the signal from a SFH2240 photodiode .

When approching my body with a synthetic pullover  or a plastic rule at about 10 cm from the pcb  the amplifier immediately saturates or get to 0 volt

I have tried 10 Mohm feedback resistor or 1 Mohm with same result ( Cf capacitance also different values without any change )

Any idea what would induce this electrostatic field dependancy ( as if I was driving a mosfet gate from 10 cm ?)

many thanks for help .

Bernard

  • 0
    Intellectual 560 points

    I forgot to mention that when the signal goes done to zero ( or up to Vss ) I can get rid of this effect by touching with my hands the small wires that I used to connect 2 nets of pcb that were missing ( mistake in design ) . This seems to discharge the electrostatic charges accumulated somewhere ?

    would these external wires explain the electrostatic dependancy ( wrapping wires styles )?

  • Former Member
    0 Former Member in reply to bernard genot

    Hello Bernard,

    Thanks for your question!  We have been a bit busy today.  But, you can expect to hear back from us tomorrow.

    Regards,

    Daniel

  • 0 in reply to Former Member
    Intellectual 560 points

    Hello Daniel,

    thanks for future help proposal but it will be no more necessary :

    I found the origin of my problem : I am using a adg1408 multiplexer to switch from one LED to another .

    On my test bench I forgot to put one of the data address pin to a potential , so it was floating and therefore sensitive to electrostatic environment .

    Solution was to connect this pin to gnd and problem is removed .

    3 days lost due to electronic basics oblivion  : never leave an entry without clear potential 

  • Former Member
    0 Former Member in reply to bernard genot

    Hello Bernard,

    Sorry to hear about this oversight, but at least the problem is now resolved.

    Please let us know if you need further assistance.

    Regards,

    Daniel