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LM5046: CS pin for secondary side current sense

Masaru Oinaga
Expert 4415 points
Part Number: LM5046
Other Parts Discussed in Thread: UCC28950, LM5026, UCC28630, UCC28782

Tool/software:

Hello, Team,

Customer contacted us about using LM5046 in their new R&D project of H-Bridge DCDC Converter. They plan to use it in current mode control.

  1. The current sense input to CS is described as an input from primary side using a current transformer (datasheet 7.4.3). Can they use CS to sense the current on the secondary side instead of primary side? 
  2. What would be the consequences or what have to be taken care of when they use CS for secondary side current sense?
  3. Any newer devices we can propose to our customer?

 The background of this inquiry is that they want to set the current to 25A with Vout=14.5V independent of an input voltage. From the datasheet, it only describes using CS for primary side current sense, which we think that they cannot control the secondary side current cannot be controlled.

Best,
Masaru

  • 0
    TI__Guru 73905 points

    Hi,

    1. Please draw a circuit to show where to you want to sense the current. Based on your drawing I can provide my comment. I am not understanding what you want to do and why not sense the current from the primary side and where to sense the current (in circuit) so I do not know how to answer you at now.

    2. Please provide your circuit drawing where to you want to sense the current.

    3. UCC28950/1

  • 0 in reply to Hong Huang
    TI__Expert 4415 points

    Hello, Hong,

    What they want to achieve is a kind of constant current (CC) operation with 25A at 14.5V, and thinks that in order to do so, will need to sense the current of a secondary side: 

    Is this feasible? What are other solutions to achieve CC/CV operation with a phase-shift full-bridge converter or isolated converter in general?

    Best,
    Masaru

  • +1 in reply to Masaru Oinaga
    TI__Guru 73905 points

    Hi,

    The current to be sensed is at its peak - when reaches peak, the primary side MOSFETs will be off. But the sensing point is more like DC current with small ripple, so the sensing can be difficult to correctly determined by the IC - the peak current thresholds and the sensing circuit components are with tolerance which make current sensing more difficult.

    It looks like you need an average current control, but LM5026 does not have this feature.

    We also do not have an average current sensing controller for phase shifted full-bridge.

    Depending on your power level, and input voltage range, UCC2870x, UCC28630, UCC28782, all these have CV CC operation. But these are for off line universal AC-DC power adapters like in personal electronics, these are isolated flyback converters.