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I'm working on a 3.3V circuit for my ARM chip, and finding it a bit difficult, determining which voltage regulator to select. Looking at for example Texas Instruments only, here are litterally thousands of voltage regulators. Being spoilt fot choice, I know I want at least the following:

  • 3.3V output
  • must have short circuit and over temperature protection
  • must be affordable
  • must be efficient

How do I select the right one, without picking that is too prehistoric.

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Current is also very important. How much current is your circuit going to draw? The ARM datasheet should be able to give you a max power supply current rating. – Stacey Anne Jan 12 at 8:53
What's wrong with the good ol' LM317? – Camil Staps Jan 12 at 9:33
According to the datasheet, the chip is drawing a maximum current of 123mA at 80MHz with all peripherals on at 25˚C – josef.van.niekerk Jan 12 at 9:36
1  
Unless you have a battery powered application and the rest circuit draws very little current the efficiency of all linear regulators is the same. And another criterium: through-hole and/or SMD? My current favourite is the MCP1702. As for current: I assume the ARM ins't the only chip, so you'll have to add the current consumed by the rest of the circuit. And what is the input voltage for the regulator? – Wouter van Ooijen Jan 12 at 9:44
I'm looking for a surface mount component and will be feeding it 5V from USB Vbus. Taking a look at the power designers now, thanks for the tip! – josef.van.niekerk Jan 12 at 9:58

2 Answers

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One way to start on this would be one of the free power design simulators provided on various manufacturer web sites.

Since you mention Texas Instruments, try their WeBench Power Designer and SwitcherPro Design Tool.

While familiarizing yourself with these tools, you will understand the additional parameters that need to be defined for optimal selection of regulator.

To address specific points in the question:

  • 3.3 Volt output: Easy to filter for, equally easy to specify as a parameter in the simulator
  • Short circuit / OVP: Again, easy to filter for, use the parametric search on the TI site.
  • Affordable: If you mean just the part, sort the parametric search by price. If you mean for the entire power regulation BoM, the simulators offer price as a design parameter.
  • Efficiency: An LDO is less efficient than a switching (buck) regulator as it must dissipate the excess voltage as heat, proportional to the current drawn. This comes at the cost of increase in BoM line items and increased output ripple

Besides the above, additional parameters must be identified, such as:

  • What is the source voltage?
  • What is the maximum current that must be supported? Add a fair margin.
  • What is the PCB area budget? If this is tight, a switcher might not be an option.
  • What is the thermal budget? If heat-sinks are acceptable, LDOs or linear regulators will help with the "affordable" parameter.
  • What is the input ripple expected?
  • What is the output ripple tolerance? Switchers inherently have greater ripple, thus also additional output filtering capacitance required.
  • What reliability requirements do you have? Greater MTTF comes at greater price.
  • Do you need to handle extremes of EMI or power surges (e.g. automobile devices)?

Once these are nailed down, the selection becomes easier. These variables are the reason manufacturers like TI have such a vast selection of parts for fulfilling what is apparently the same purpose.

Further, this answer maybe of use to you.

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I'm actually finding the parametric search for RS Components quite powerful, thanks for the useful advice. – josef.van.niekerk Jan 12 at 10:28
up vote 1 down vote

Using the comments and answers supplied, I have used RS Components' website to select and filter out a selection of voltage regulators. The criteria I specified was as follows:

  • Maximum Output Current : 0.4A (I'm powering from USB 5V Vbus)
  • Output Voltage : 3.3V
  • Maximum Input Voltage : 5.5V
  • Accuracy : +/-0.5%
  • Mounting Type : Surface Mount

See the results here.

The selection came down to the Texas Instruments TPS73633 regulators, and I'll consider using the small 3mm x 3mm VSON EP package, depending on how brave I feel in regards to soldering it to by board later.

I'm not going to accept my own answer, but I just thought it would be cool to share what the outcome was.

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And the results are ROHS compliant. :) – josef.van.niekerk Jan 12 at 10:49
General norm around here is to add the conclusions as an "Update" edited into your original question, perhaps separated by a ruler. This isn't mandatory, just suggested, as it helps future viewers finding this question, to see the whole thing at a glance. – Anindo Ghosh Jan 12 at 12:13

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