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LM5575: request schematic review

TS Yang
Genius 4800 points
Part Number: LM5575
Other Parts Discussed in Thread: LM5116

Hi,

The Inverting Power Supply was designed using the TI's LM5575.

At the schematic in the attachment below, Inverting power supply of -13VDC and -16VDC output is designed respectively.

Input and output load conditions are listed, and the component values around the LM5575 have been calculated but not accurate, so we will ask TI to fix and review the circuit.

We designed -26VDC, -42VDC and -58VDC output by stacking -13VDC and -16VDC Inverting Power Supply.

We ask TI to review whether this part is working properly.

Please refer to the Schottky Power Rectifier datasheet used in the circuit.

8422.LM5575_CIRCUIT.PDF

2146.MBRS3100T3-D.PDF

thanks,

TS

  • 0
    TI__Mastermind 23815 points
    Hi,

    Please allow us some time to review the schematic

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    TI__Mastermind 23815 points
    Hi,

    I believe the bottom LM5575 (U25) will see a voltage of 106V across VIN and GND. The U24 will see 86V accross VIN and GND and this will violate the abs max of the LM5575

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Genius 4800 points
    So what product should I use to support -58V?
  • 0 in reply to TS Yang
    TI__Mastermind 23815 points
    If your input is 48V, then you need a converter that can handle 48+58 = 106V. So far i have not seen an integrated switch that can do beyond 100V input. You might want to go with a flyback controller (isolated topology)
  • 0 in reply to Arief Hernadi
    Genius 4800 points

    Hello TI,

    Your answer is that, the U24 and U25 have a voltage difference between VIN and VOUT of 90V and 106V, respectively, of the LM5575. It says that it can not be used beyond Input Voltage (75V).

    The voltages set for U24 and U25 are -16V and the voltage across VIN and VOUT is Is it 64VDC with 48VDC + 16VDC?

    The purpose of stacking is to set the VIN + VOUT voltage to the LM5575's Max. It is to make several voltage of -13V and -16V which do not exceed the input voltage and to make the desired voltage by connecting with Serial.

    The input voltage range of the power module used in the EVM circuit diagram in the attached file is also Max. 80V. Stacking is done by using diodes in each connection between power modules.

    If follow TI's suggestions above, it means I can not use the power used in EVM Board.

    In my opinion, considering the GND pin of the LM5575, I think that 48VDC + 16VDC is the voltage applied to the LM5575.

    If the above is incorrect, we will change the design direction with non-isolated flyback controller.

    So, please review and reply.

    TS

  • 0 in reply to TS Yang
    Genius 4800 points

    2352.EVM_Power.pdf

    0647.SW001A0C91Z.PDF

    sorry, I missed to attach EVM shematic.

    TS

  • 0 in reply to TS Yang
    TI__Guru**** 191445 points

    It does not matter about the stages.  It is ViN vs the IC ground which is -Vin for the inverting buck boost.  So fro 48n V input the maximum negative output for LM6675 is -27 V.  I agree, you should be looking at a flyback solution.

  • 0 in reply to JohnTucker
    Genius 4800 points
    Hi,

    I honestly do not understand it well.
    In the schematic above, the ground is not connected to LM5575 so I think the IC ground should be -16 V.
    Please explain more details about this, because I do not know the block inside device.

    TS
  • 0 in reply to Arief Hernadi
    Genius 4800 points
    Dear Arief Hernadi,
    We can not use isolated topology because of structural problems.
    Can you recommend any non-isolated solution at TI?
  • 0 in reply to TS Yang
    TI__Mastermind 23815 points
    Hi Yang,

    Unfortunately i have look on the controller side as well as switch side and i could not find any IC that can handle beyond 100V

    The reason it will be more than 100V is because the last bottom converter when you stack it up it will be -16V from the previous negative output and not from GND
  • 0 in reply to Arief Hernadi
    TI__Guru**** 191445 points

    If you cannot use an isolated solution like a flyback, you could consider bucking your 48 V input down to a lower voltage, say 12 V.  Then you would have enough headroom to get your - 58 V output.  Also, I would recommend at that point to reference each of your converters to ground rather than the output voltage of the rail of the next higher (less negative) circuit.

  • 0 in reply to JohnTucker
    Genius 4800 points

    Hi,

    As suggested by TI, there are questions about designing -26VDC, -42VDC and -58VDC after stepping down 48VDC to 12VDC.

    The attached document below is related to "Creating an Inverting Power Supply from a Step-down Regulator" by TI.

    slva317b.pdf

    The contents of this document are as follows.

    Applying the formula above with the LM5575,

    Vin = 11 ~ 13VDC, Vout = -26VDC

    Icl = 1.8A,

    ILripple = 1.8 x 0.25 = 0.45A, Dmax = 0.7 into the equation,

    0.47A, which is less than I think(Iomax = 0.7A), so the LM5575 can not be used.

    If the above calculation is correct, I think that a Buck Converter of 3A / 75VDC or more which has larger current capacity than LM5575 is needed.
    Please confirm this part as TI side and recommend other parts if you can not use LM5575.

    So, please review and reply.

    thanks,

    TS

  • 0 in reply to TS Yang
    TI__Guru**** 191445 points
    Yes your equation is correct. You can look for a higher output current part (I do not personally support anything that meets your input voltage range requirements). You may want to consider a controller.
  • 0 in reply to JohnTucker
    Genius 4800 points

    thanks for your answer.

    Please recommend TI Controller device which can produce -26VDC, -42VDC and -58VDC Inverting Power Supply.

    Each power capacity is Max. 0.7A.

    The input power is +48 VDC, but can be lowered to +12 VDC if needed.

    So, please review and reply.

    TS

  • 0 in reply to TS Yang
    Genius 4800 points
    Hello TI,
    Can you recommend a TI's controller device for us?
  • 0 in reply to TS Yang
    TI__Mastermind 23815 points

    Hi TS Yang,

    Based on my search the highest voltage that our controller can handle is 100V which is LM5116

    Thanks

    -Arief