650W Buck Boost converter with current sense transformer?

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treez

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Hello,
We are doing a 650W synchronous buckboost converter (as a variable current regulator) using LT3791-1 controller.
Max current is 25 Amps output. (Vin = 18 to 32V), fSW = 200KHz.
We wish to use a current sense transformer instead of a resistive current sense.
However, the LT3791-1 senses the current that flows from drain to source when in boost mode, and from source to drain (the other way), when in buck mode.
Will it be possible to use a current sense transformer in this case.?

When Vin is very close to vout, the LT3791-1 operates in "buckboost" mode and the synchronous fets are switched so as to increase the current deviation, -will the current transformer be able to manage this?

LT3791-1 Datasheet:
http://cds.linear.com/docs/en/datasheet/37911fa.pdf

LTspice sim and schematic attached
 

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Probably not. As you observe, the current needs to be sensed in both positive and negative directions, so a CT with a rectified output won't work. You need a truly broadband current sensing scheme for this, so stick with the sense resistor.
 
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I understand that the circuit tries to solve the varying polarity problem by using two current transformers (which is a somehow cumbersome way to get the measurements), but you get only a duty-cycle dependent varying share of the current seen by the original shunt. Thus I think, it will never work as expected by the controller.
 
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