Current regulator regulates using external opamp feeding into pwm controller?

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treez

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Hello,
We are doing a variable output current regulator, for max 20Amps.
We feed the feedback signal back into the Vc pin of the LTC3791-1 PWM controller.
Is this OK?, or should we use the FB pin for the feedback?
(we have an external opamp error amplifier on the current sense resistor)

LT3791-1 datasheet
http://cds.linear.com/docs/en/datasheet/37911fa.pdf
 
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In theory either the Vc or FB pin can work. However realize that depending on which one you use, you need to make sure your feedback is still negative, so it may be necessary to use two external inverting amps if you use the FB pin. Also if you directly drive Vc then you will be bypassing a lot of the fancy protection and startup features built into the controller, which may or may not be desirable.
 
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Thanks, by the way, the schematic is as follows...

-does the 1K resistor in series with the Vc pin look to be well sized, may I ask?

(LTspice sim also attached)
 

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  • LT3791-1 _current regulator.pdf
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  • LT3791-1 _850W _VIN=28V +D=0.18_vcreg.txt
    10.9 KB · Views: 95

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