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LT3082/LT3092 500+kHz disturb causes output offset.

Category: Hardware
Product Number: LT3082

We are using the LT3082 in current source configuration for an ICP sensor (4.5mA). The bandwidth of the signal is < 1KHz. We have a problem that when high frequency noise (500kHz-1MHz) is coupled to the output of the LT3082, the regulator generate low frequency noise, like it demodulates the noise signal. (Low frequency noise is in band so it affects our signal processing).

With reference to the LT3092 datasheet we started with the circuit of Figure 1: "Using the LT3092 as a Current Source". Then we tried to follow the directions in paragraph "Stability and Frequency Compensation", so we added a 1nF capacitor parallel to RSET and another (Ccomp) between in and out, but it only get worse.

Questions:

  1. Are LT3082 and LT3092 the same component? If not, what are the differences in our application?
  2. Why our circuit is so sensitive to high frequency noise? What can we do to avoid this behaviour.

Best regards

Parents
  • The LT3082 and LT3092 are the same part.  The datasheets are not identical, though.  I don't know enough about your circuit to try it myself in the lab.  My guess is that your noise occurs at a low-frequency repetition rate that is within your measurement band but the noise actually has high-frequency content that the LT3092 cannot reject.  My advice is to observe the noise in the time-domain with your o-scope and try to filter or shield the noise at its source.  Ferrites plus capacitor filters or even RC filters can be used for the filtering purpose.  The compensation capacitors you mention are just for stability and not for filtering.  My guess is that your circuit does not have a stability problem, but you can check just by doing a line transient and seeing if the current rings or is damped.

  • The LT3082 and LT3092 are the same part. The datasheets are not identical, though. 

    The price neither! Joy

    I think you're right. We got a big improvement with a LC filter. We have still a problem at its resonance, but I'm confident we can overcome it with different component value.

    Ferrite would be great but 500kHz is too low.

    Thank you.

Reply
  • The LT3082 and LT3092 are the same part. The datasheets are not identical, though. 

    The price neither! Joy

    I think you're right. We got a big improvement with a LC filter. We have still a problem at its resonance, but I'm confident we can overcome it with different component value.

    Ferrite would be great but 500kHz is too low.

    Thank you.

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