• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 1299 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28950: Secondary Synchronous Rectification under UCC28950 in Primary side

Koshi Ninomiya
Expert 5435 points
Part Number: UCC28950
Other Parts Discussed in Thread: PMP8606, UCC24612, UCC28951, UCC21520, LMG1020, UCC27611, LMG3411R050, LMG3410R050, PMP20657

Hi Team,

My customer is considering to use UCC28950 for the following application by placing it on the primary side.
 - Phase-Shifted Full-Bridge application
 - UCC28950 on the primary side
 - Secondary synchronous rectification is done by another controller
 - VIN: 300V typ
 - Vout: 15V typ
 - Iout: 150A max

For the primary side application, I showed the PMP8606 to them as reference.
For the secondary side application, they want to use a Synchronous Rectifier Controller IC because of high output power.
Q1. Are there any concerns to use a external Synchronous Rectifier Controller IC in the secondary side compared with the synchronous rectification feature of UCC28950 inside?

Q2. What is the recommended Synchronous Rectifier Controller IC for this kind of application?
       How about the UCC24612 High Frequency Synchronous Rectifier Controller?

Q3. If GaN FET was used for synchronous rectifier switching device, are there any guidelines to use it?

Thank you.

Best Regards,

Koshi Ninomiya

  • 0
    TI__Mastermind 25570 points

    Hello Ninomiya-san

    I'm travelling on business until Wednesday - I will try to answer your question earlier but I cannot guarantee it.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points

    Hello Ninomiya-san

    I'm working on a reply - I hope to have it ready on Monday.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points

    Hello Ninomiya-san

    A few points first –

    The newer UCC28951 is a 100% compatible, drop-in replacement for the UCC28950 and I would suggest that the customer select the newer part. The differences are described in the application note at http://www.ti.com/lit/an/slua853/slua853.pdf

    Both the UCC28951 and UCC28950 are mainly intended for use on the secondary side of the isolation barrier. This gives easier system integration – synchronisation, on/of control, current sharing for example and removes the need for an opto-coupler in the feedback path.

    However, it is certainly possible to use this part as a primary side controller.

    The SR drives generated by the UCC28951(0) can be transferred to the secondary by an isolated gate driver such as the UCC21520 http://www.ti.com/product/UCC21520 . This has the advantage that the SRs can be disabled at light loads for improved efficiency and eases the design of the secondary side PCB layout because there is no need for careful sensing of the drain-source voltage. The PMP8606 schematic can be easily changed to include the UCC21520 isolator/driver.

     

    A1/         I think it would be a much, much better solution to use the on-board SR drives generated by the UCC28951(0) because the SR drives are actively controlled by the UCC28951(0) rather than being generated independently by a different IC. I would always worry about noise causing the external SR controller to switch incorrectly and would take exceptional care to ensure a low noise PCB layout for the SR controller. Honestly, I can see no advantage to using an external controller.

     A2/         The UCC24612 would work ok but my opinion is that using the on-board SR signals from the UCC28951(0) is a much better solution.

     A3/         The UCC21520 is not really ideal for driving GaN devices. In that case I’d suggest using the ISO7740F signal isolator (F option, outputs default LOW) and a GaN driver IC like the UCC27611 or LMG1020 . You can see an overview of the GaN driver portfolio at http://www.ti.com/power-management/gate-drivers/gan-fet-driver.html

    Whether GaN is better than Si or not depends on a lot of factors. To be honest, I think that at 15V out and at switching speeds of 100kHz or so there is little benefit to moving to GaN for the SRs.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    TI__Expert 5435 points

    Hi Colin-san,

    They currently have the following solution,
     - Phase-Shifted Full-Bridge application
     - Control IC on the secondary side
     - Drive signals are transferred to the primary side through photocoupler, and 4 GaN FETs are driven by driver IC
         --> Drive signal delay occurred by photocoupler and driver IC and it is about 100nsec
         --> Secondary synchronous rectification switching timing is adjusted by gate resistor
     - Switching frequency is 80kHz to 100kHz
     - VIN: 300V typ
     - Vout: 15V typ
     - Iout: 150A max

    To handle the drive signal delay from the secondary to the primary, they are considering the following new solution,
     - Phase-Shifted Full-Bridge application
     - UCC28951(0) on the primary side
     - 4 GaN FETs on the primary side (Must)
     - Switching frequency is targeted around 300kHz
     - Secondary synchronous rectification is done by another controller without photocoupler due to space limitation
     - VIN: 300V typ
     - Vout: 15V typ
     - Iout: 150A max

    Q4. When switching frequency is increased to around 300kHz, what should they be careful about under the new solution?

    Q5. Can LMG3411R050 (600V, 50mohm, GaN Power Stage) be used with UCC28951(0)?

    Q6. LMG3411R050/LMG3410R050 has IDS (DC Drain-Source Current (Tj=125℃)) as Max=12A at recommended operating conditions, although it has IDS.pul (Drain-Source Current, Pulsed) as Max=130A at absolute maximum ratings.
           Why is the IDS 12A (max) such lower?

    Thank you.

    Best Regards,

    Koshi Ninomiya

  • 0 in reply to Koshi Ninomiya
    TI__Mastermind 25570 points

    Hello Ninomiya-san

    A4/    Switching at 300kHz is possible - the PMP20657 runs at this speed - http://www.ti.com/tool/PMP20657

    A5/    The LMG3411R050 device can be used with the UCC28951(0) - The LMG3411R050 includes on-board drivers. The 0/10V output of the UCC28950 OUTx pins will need to be attenuated to the 3V to 5V recommended IN level for the LMG device.

    A6/   The pulse current rating is for a pulse < 100ns so there is little total energy in the pulse and there is little heating associated with this pulse because of the thermal inertia of the device. The IDS rating is for a continuous pulse and the chip will reach a thermal equilibrium.

    Regards

    Colin