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TPS5450: inverted and non inventer supply using TPS5450

Deepa
Prodigy 60 points
Part Number: TPS5450
Other Parts Discussed in Thread: LM61460, , TPS54060

dear expert,

can you please cross-check the following PSU is according to the datasheet.

is there any problem with GND for -15V ?

TIA....

  • 0
    TI__Mastermind 41790 points

    Hi,

    Have you also tried looking at the alternative LM61460 device? The TPS5450 is a relatively older device and it is recommended to move to newer devices if supply is available.

    Please refer to this app note (https://www.ti.com/lit/an/snva856a/snva856a.pdf) for more details on converting a buck into an inverting buck boost (IBB) design.

    For the IBB designs U104 and U106, how much load current is expected from the application? Also can you fill out what the inductor values are? It is not detailed in the schematic.

    Following Section 4.1 of the app note, the voltage stress the TPS5450 can experience should be limited to the maximum input voltage range. This means that for a -15V output rail, the maximum input voltage should be no more than 20V. 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 60 points

    For the IBB designs U104 and U106, how much load current is expected from the application?

    >>>> U104/ -5v@2A , U106/ -15v@0.15A , U102/ 5v@4.5A

    Also can you fill out what the inductor values are? It is not detailed in the schematic.

    >>>>L7/L8/L9 = 10uH,5A,21mohms

    Following Section 4.1 of the app note, the voltage stress the TPS5450 can experience should be limited to the maximum input voltage range. This means that for a -15V output rail, the maximum input voltage should be no more than 20V. 

    >>>>Input supply is nominal=20v, while output is fixed =-15v. so is this okey with TPS54060 ?

    >>>> for whole design, the common ground is used...is that okey? can you share the layout guide also...

    thanks..

  • +1 in reply to Deepa
    TI__Mastermind 41790 points

    Hi,

    Yes the three designs you've shown should be okay. 

    There is no issues with using common ground for all three designs.

    Regards,
    Jimmy

  • 0 in reply to Jimmy Hua
    Prodigy 60 points

    thanks..one more Q about the U104/TPS5450. TP/pin9/powerpad should be ground here ?

  • +1 in reply to Deepa
    TI__Mastermind 41790 points

    That's a good catch!

    For U104, Pin 9 is the IC return path of the switching device. For a IBB topology, this pin will be the negative output (-VOUT). 

    Please have the schematic changed such that pin 9 is connected to the -5V rail.

    Regards,

    Jimmy