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Positive supply with strange behaviour

Category: Hardware
Product Number: LT3097

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On our board we have a LT3097 (U42) that drives some analog filters and other low power downstream devices.

See the attached schematic excerpt.

We see that the +ve output is not correct whenever the -ve output is enabled (at ENN_UVN).

We have tried temporarily removing L26 and L27 (output ferrites) and powering downstream circuits from an external supply.

This works perfectly, with the downstream drawing around 40-60 mA from each of the external +5 and -4.5 rails.

We also tried shorting the current limit resistors R150 and R154 but this does not improve the situation.

In addition, removing the ferrites and connecting OUTP to OUTN with a 80 ohm load resistor.

Please - we need some further ideas for debugging this problem.

Thanks

David