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UCC28070-Q1: Replacing CT with shunt

Part Number: UCC28070-Q1

Hi Team, 

One of the customer is currently using UCC28070-Q1 for an interleaved PFC boost converter. They are using 2 current transformers in each leg of the PFC similar to App note figure 3: https://www.ti.com/lit/an/slua896/slua896.pdf 

But the above Current transformers are increasing BOM cost, so can a current shunt resistor of 1 milli ohms be used in each leg for the PFC  MOSFET’s current measurement (followed by an op amp based filter and voltage follower before feeding the signal to the CSA/CSB pins)?

Regards,
Naveen

  • Hi Naveen, 

    It should be possible to use shunt resistors the switching leg (with buffering and proper scaling of the signal to satisfy CSx levels). However, I have been unable to find an example of this being done successfully, so I am hesitant to recommend this approach.

    Keep in mind, this will impose an efficiency penalty due to the IxR loss through the shunts. To reduce the loss, there will need to be a balance between the smallest shunt value as possible (and amplifying the signals accordingly), while also being mindful of signal-to-noise.