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I have one working PCB which has three different Voltage Rails: 3.3V, 4V and 1.8V. They are generated using three separate step-down buck converters. The input voltage to all the converters is a single DC Power Supply (12V).

  • Buck Converter Generating 4V powers 4G LTE Module (Load 2.5A)
  • Buck Converter generating 1.8V powers LoRa IC SX1301 (Load 1A)
  • Buck Converter generating 3.3V powers iMX6ULL System-on-module (Load: 3A)

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These three different buck converters are occupying alot of PCB space and increasing the BOM. I am thinking to implement single IC solution for my system. A quick google search landed me on two solutions.

  • A Triple Step-Down Converter from TI (TPS6526x)
  • Using a single Buck Converter to generate multiple voltages. (The link is over here).

What should I consider? Is there any different solution other than listed above?

EDIT: The LoRaWAN IC is SX1301 and it requires 1.8V power supply.

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  • \$\begingroup\$ Can’t you use the same 3.3V supply for at least the SX1231 and iMX6ULL? (maybe also the unnamed LTE modem) \$\endgroup\$ – Michael Dec 29 '18 at 19:38
  • \$\begingroup\$ Sorry. The IC is SX1301. \$\endgroup\$ – abhiarora Dec 30 '18 at 4:17
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    \$\begingroup\$ The single point option for all three power supply using TI webbench works, as long as you use all the components mentioned in their BOM..only problem I find is if the IC fails, all three power lines will go for a toss as also pointed out in one of the answers. Do look deeply for Reliabilty of IC, along with operating temperatures when you go for full load. \$\endgroup\$ – AKR Dec 30 '18 at 10:45
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The triple converter gets you some space savings while maintaining the basic simplicity of buck regulators. However, the chip now is a single point of failure. Multiple outputs from one switching stage will save more space. However, the magnetics no longer are simple inductors so the added design and development time might eat up or exceed the BOM savings. Unless you're talking about high volume, I'd go with a triple controller. I prefer Linear Tech, but TI should be fine.

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  • \$\begingroup\$ Where to start for magnetics of single switching stage? \$\endgroup\$ – abhiarora Dec 29 '18 at 18:15
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    \$\begingroup\$ Triple converters also often have startup/shutdown features that make it easier to keep power sequencing constraints like "the 5V rail may not drop more than 0.3V below the 3.3V rail at any time". \$\endgroup\$ – Simon Richter Dec 29 '18 at 18:17
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There are many triple output SMPS on the market and in Design Reference sites like Analog, LTI, TI but they tend not to be give out the larger power designs that are worth more and may have OEM IT property tricks or custom magnetics.

You need to assess your cost, performance, skills, time and qty tradeoffs then consider everything including AC to DC, EMI, performance, cost and reliability.

If you have the skills then you will have at least a 1 page list of all specs.

If you do then expand it to at least 5 pages and do some due diligence cost analysis and see if you can achieve $5 in volume for 22W from AC to triple output DC like this possibility. enter image description here

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