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TPS54360: questions about inverting buck-boost topology

TS Yang
Genius 4800 points
Part Number: TPS54360
Other Parts Discussed in Thread: LM5576, LM5575

Hello,

First of all, the history is started from "Stacked-Cuk", and jumped to this forum from below thread.

https://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/610920/2257099

Q1. Please recommend the appropriate product for the following specifications.

1. Vin : 48V
2. Vout : -16V
3. Iout : 1A
Q2, I wonder if the following design considerations are essential for inverting buck-boost topology.
1. nonsynchronous
2. peak current mode control
3. COT
thanks,
TS
  • 0
    TI__Genius 11085 points

    If you use a buck converter as an interting buck-boost converter, the supply voltage seen by the buck is VIN+|VOUT|. In your application, the supply voltage to the buck converter is equal to 48+16 = 64V. The TPS54360 is a 60V max voltage device.

    I'd suggest LM5575 (75V 1.5A device) or LM5576 (75V 3A device) for this application.

    -Yang 

  • 0 in reply to YangZhang
    Genius 4800 points

    Hi Yang,

    The Inverting Power Supply was designed using the recommended 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.

    LM5575_CIRCUIT.PDF

    MBRS3100T3-D.PDF

    thanks,

    TS

  • 0 in reply to TS Yang
    Genius 4800 points
    Hello TI,
    Do you have any update for me?
  • 0 in reply to TS Yang
    TI__Genius 11085 points
    When you have -42V and -58V rails as the -VOUT, and +48V as VIN, the supply voltage seen by the LM5575 is VIN+|-VOUT|= 90V and 106V. They are out of the supply voltage range of the device. Even when -VOUT=-26V, VIN+|-VOUT|= 74V is too close to VINmax of this device, not recommended to operate there.

    -Yang
  • 0 in reply to YangZhang
    Genius 4800 points
    So what product should I use to support -58V?
  • 0 in reply to TS Yang
    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.

    SW001A0C91Z.PDF

    EVM_Power.pdf

    So, please review and reply.

    TS

  • 0 in reply to TS Yang
    TI__Genius 11085 points
    Your +48V and -58V are referred to the same ground. For the LM5575, the input is connected to +48V and AGND/PGND is connected to -58V. So the voltage difference seen by the IC is 106V.

    Please do not have two threads discussing exactly the same issue. I will close this one. Please continue your discussion on the other thread, where John and Arief are both helping you.

    Thank you,

    Yang