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LM5022: Alternatives for LM5022 for isolated flyback design

Neo.Wang
Intellectual 980 points
Part Number: LM5022
Other Parts Discussed in Thread: LM5156, LM5122, LM51561

Tool/software:

Hi TI experts,

I used LM5022 in my old projects for isolated flyback design, the input is 9-60V and output is 12V/2A.

But LM5022 seems simple for protection function and the primary OCP is hiccup, but not latch off.

Can you advise alternative controller for isolated flyback design with below features?

1. Can support wide input voltage range 9-60V

2. Can replace LM5022 with minor external component (transformer/FET/Rsense,etc) changes to existing design

3. With more protection function like OC/OV (Latch off mode is preferred)

4. Can be used for secondary Synchronous rectification to improve the conversion efficiency

Please kindly advise.

Neo

  • 0
    TI__Intellectual 2426 points

    Hi Neo,

    Thank you for using the E2E form.

    LM5022 only has cycle by cycle peak current limit protection and it doesnt have Hiccup mode.

    For the alternatives, LM51561( Vin max upto 60V) is the best alternative. This device has Hiccup mode protection. We do not have devices with Latch off mode. 

    For the secondary Synchronous rectification,  LM51561 cannot be used. As an alternative, you could use LM5122 with isolated driver for secondary side switch.There are also dedicated synchronous flyback devices for this. 

    Please let me know if you have any further questions. 

    Best regards,

    Mounika

  • 0 in reply to Mounika Girish
    Intellectual 980 points

    Hi Mounika,

    Thanks for feedback.

    For LM5122, which isolated driver can be used for secondary synchronous rectification?

    For  dedicated synchronous flyback devices, could you share some P/Ns?If the input voltage range is 45V-56V only, any other alternative?

    Can we implement the OVP protection for isolated flyback design?

    Thanks

    Neo

  • 0 in reply to Neo.Wang
    TI__Mastermind 19715 points

    Hello Neo

    The LM5122 does support a synchronous flyback topology.
    See the following reference design: 
    www.ti.com/.../PMP9256

    Also, with a simple additional Zener diode, the LM5122 will also support latch off.
    See chapter 7.4.3 in the datasheet:
    If a 3-V Zener diode is connected in parallel with the RES capacitor, the regulator enters into the hiccup-mode off mode and then never restarts until UVLO shutdown is cycled.

    To add an additional overvoltage protection, as shown in chapter 8.1.5 of the LM5122 datasheet, you would need to replace the transistor with another optocoupler to assure isolation. 

    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Intellectual 980 points

    Hi Harry,

    Thanks for details.

    If the fiyback is designed for 9V-60Vin, and when operate at 60V, it should be able to output higher current without the transformer saturated, is my understanding correct?

    Thanks

    Neo

  • 0 in reply to Neo.Wang
    TI__Mastermind 19715 points

    Hello Neo,


    You are right, the higher the input voltage, the lower the peak current through the transformer.
    So, you can select a transformer with lower current ratings. 

    But please make sure that you will calculate the peak current according to the lowest worst case input voltage. 


    Best regards
    Harry