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LM5050-2 drive two back to back FET's

Shahzad Malik97479
Intellectual 295 points
Other Parts Discussed in Thread: LM5050-2, TPS2411

Can the TI LM5050-2 OR-ing controller drive two back to back FET's to fully disconnect input and output? Such as the device below?? 

  • 0
    TI__Mastermind 40100 points

    Hi Shahzad,

    There is no issue with using the LM5050 in this configuration. This typically is what we recommend to prevent reverse current flow.

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Prodigy 70 points

    Hello Darwin, About proper implementation of connecting two back to back FETs with LM5050, I'm wondering about two things: 1. I assume that Vs pin of LM5050 should be directly tied to the input Vin (pls see schematic in attachment, IC U2). Can this be confirmed? 2. Since body diode of Q2 (schematic in attachment) does not allow current flow, there will be no deterministic voltage drop across IN and OUT pins of LM5050. Will in that case LM5050 still start to drive the GATE high in order for the Q2 to start conducting (and accordingly Q3)? Is there any other comment regarding implementation presented in the schematic (circuitry for enabling U2 is not shown). Regards, Jovan

  • 0 in reply to MTD
    Intellectual 280 points

    Hello MTD,

    Did you ever figure out if the circuit you proposed was functional?  I am interested in using the same device for the control of back-to-back FETs and it'd be great to confirm that this implementation works.

    Thanks,

    JR

  • 0 in reply to Jessica Riley1
    Prodigy 70 points

    Hello JR,

    I was hoping that TI will provide a response.

    MTD

  • 0 in reply to MTD
    TI__Mastermind 40100 points

    MTD, JR,

    VS can be connected to VIN as stated on page 2 of the datasheet.

    There should be no issues using the LM5050 in bidirectional blocking circuit.

    TPS2411 is a similar device and has this example on page 22 of the datasheet.

    http://www.ti.com/product/tps2411

  • 0 in reply to Darwin Fernandez
    Prodigy 60 points

    Hello,

    I'm coming into this thread a bit late, but I have the same question. If we were connecting back to back NFETs to the LM5050

    Would it be connected like in the attached schematic?

    Visio-LM5050 dual FET.pdf

  • 0 in reply to Jim Hall
    TI__Mastermind 40100 points
    Hi Jim,

    I'm sure MTD, Jessica, or Shahzad can comment if they were able to find a workable solution.

    However, unfortunately, after looking into the IC's performance a bit closer, we don't believe this solution might work with the LM5050.

    Instead, we highly recommend looking into the TPS2411. Its datasheet shows this type of implementation in page 22 of its datasheet.
  • 0 in reply to Darwin Fernandez
    Prodigy 60 points

    Hi Darwin,

    The problem with using the TPS2411 is the voltage rating. We are working with 28V and need the higher rating of the LM5050. Is the issue the limited gate drive capability of the LM5050? If so would adding an amp stage with some current gain on the gate pin solve the issue?

    Thanks,

    Jim

  • 0 in reply to Jim Hall
    TI__Genius 12380 points

    Hi Jim,

    I would recommend starting a new E2E thread with some information on your application requirements (voltage range, current, output capacitance and what features you need such as reverse current shutdown, overcurrent protection, overvoltage/surge/undervoltage protection, etc).

    If you need back-back FETs and some of these features, perhaps this two-chip solution, tested TI Design would be of interest::

    Thanks!

    Alex