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LTC1666 Application note

Category: Hardware
Product Number: LTC1666, LT1809, LT5400-3, LT3032
Software Version: -

Hi! I implemented the app note dorm figure 7 on a PCB. The differences are: - I have 50 ohm resistors for the conversion crom IA/IB to VA/VB - for the LT1809 difference amp i use your LT5400-3 (gain=10) - i changed by mistake IA and IB , VB goes to Vminus, VA goes to Vplus   My Pcb was broken, the output seems to oscilate. By random i put my Finger on the LT5400 And the output like magic appear corectly. I tought that i need a capacitor in the opamp feedback and by mistake i put it between the output and VB, and it worked a time. And now Any time i put my Finger on that capacitor wich is 47 pF the PCB is working. I Tried to put it between Vminus And output But it doesn t work that good. Can you help me please ? It s a part of my degree project witch i am presenting tuesday.
ADI Part Number: LTC1666

  • Hi Giulia,

    Good day. Can you provide us with your actual circuitry and layout so we can have a clear insight into the problem? It would also be helpful if you could provide us with a plot of the inputs and expected output. Thank you.

    Regards,

    Gilbeys

  • I suggest simulating the circuit in LTSpice. LT5400 and LT1809 are available in the libraries. For LTC1666, use the equivalent circuit shown in Figure 3 of the datasheet, with ideal current sources. This will give you an idea of the expected output and the conditions for oscillation.

    A damaged circuit may seem to work under certain conditions, and return to oscillation when the configuration changes.