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LMR14030: Power distribution over 3 meter cables

Benjamin
Intellectual 290 points
Part Number: LMR14030
Other Parts Discussed in Thread: TPS65131,

Tool/software:

Hello, I am looking for some advice on power distribution.

I am building an audio installation, and I need to power our "devices" in groups of 6. The devices are usually powered by 5V from a USB-C connector, and each draw a maximum of 0.3A. There are TPS65131 converters on the input of the devices, similar to the generic schematic in the datasheet.

I would prefer not to use a USB power hub and instead power them from a 15V rail which I already have for other signals which are also being sent to the devices. The cables will be approximately 3 meters long though. My idea was to use a single Buck converter like LMR14030 to create the 5V rails, and then distribute the 5V lines to the devices over 3 Meter cables. These are audio devices so low noise is important, but the devices already have somewhat good filtering with LDOs following the TPS65131. The "Backup" outputs are just for reserve in case I want to add 2 more devices.

So my questions.

  1. Is a single LMR14030 (or similar) a good solution for powering all 6 devices, or would it be better for each of the 8 outputs to have their own lower power buck converter?

  2. What type of filtering (if any) should I put on the PSU outputs? I currently just put in some ferrite beads, but I would appreciate some help on how to thoughtfully design that part.

  3. Would an LDO after the LMR14030 be a good idea since I want to minimise noise?

Thanks!

  • 0
    TI__Mastermind 22260 points

    Hello,

    The LMR14030 can supply the total 1.8A load for these LDOs.

    Depending on the resistance in the cable, you may need to set your input voltage slightly higher than what the LDO needs to account for losses along the cable. Make sure that the FB path of the buck converter is connected directly to the output capacitors of the LMR14030 nearby the converter.

    The 3 meter cable will represent a lot of inductance on the input of the LDOs, so you will need to have adequate damping capacitance at the point of load for a stable output.

    I recommend reaching out to the LDO team specifically for recommendations on how a 3 meter cable will impact the input of those devices.

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Intellectual 290 points

    Hi Ridge,

    Ridge Lahti said:

    The 3 meter cable will represent a lot of inductance on the input of the LDOs, so you will need to have adequate damping capacitance at the point of load for a stable output.

    I recommend reaching out to the LDO team specifically for recommendations on how a 3 meter cable will impact the input of those devices.

    The input of the load devices is actually a boost converter (TPS65131), not an LDO. The LDOs come after.

    Are you able to give suggestions for adequate damping since the 3 meter cables are feeding a boost converter?

    Also what do you think about my addition of Ferrite beads on the outputs? I just saw it in another reference design but not sure if it might actually make it worse.

  • 0 in reply to Benjamin
    TI__Mastermind 22260 points

    Hello,

    The ferrite beads may help with noise, but they will not help reduce voltage ringing from the additional inductance in the cables.

    For the boost converter input, you will need to consult the boost converter product line for how to best damp the input coming to the TPS65131.

    I recommend opening a new thread for that device specifically.

    Best regards,

    Ridge