VIOC-Pin at the LT3094

Question

Hello, 
 
 I have a question about the VIOC-Pin at the LT3094. Currently I am using the TPS65131 from Texas Instruments as a DC-DC-Converter. I have connected the LT3094 as a post-regulator at the negative output of the DC-DC-Converter. The positive output is connected to the LT3045. Unfortunately the LT3094 gets warmer than the LT3045. I suggest that this is caused because the VIOC-Pin at the LT3094 is not connected to the negative Feedback-Pin of the DC-DC-Converter. The resistor values are calculated from voltage at the Feedback Pin but at the DC-DC-Converter its typically 0 V, so I am not able to calculate the values. Currently the LT3094 converts the -15 V from the DC-DC-Converter to -12 V. 
 
 How do I connect the VIOC-Pin to the DC-DC-Converter?

Thank you ! 
 
 Yours sincerely 
 
 Seeran Raveendran

ARad · Answer

I don't consider myself a VIOC expert and I don't have any more time to spend on this, but this is my input: Essentially, you need to level shift the VIOC output of your LT3094 to the VREF pin of your TI part. The closest ADI part I have to check using an LTspice simulation is the LT3462 so I uploaded my simulation file and I show the simulation circuit and results in the image below.

sim ckt and result_0.png

3462 LT3094_0.zip

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VIOC-Pin at the LT3094

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