I'm designing a power supply that I would like to have a USB power output for charging/powering USB devices.

In an effort to reduce risk and design time, I'm looking at mounting a DC/DC converter on my PCB. I'd like to be able to supply >= 2A to support fast charging applications and for future-proofing.

The cheapest converters that fit the bill seem to be point-of-load modules (e.g. http://uk.rs-online.com/web/p/non-isolated-dc-dc-converters/6894703/).

I understand that these are meant for powering known loads (FPGAs, DSPs etc.) internal to the design.

Are these modules suitable for powering "unknown" loads down a cable?

You may assume that I have taken care of the other considerations with regard to meeting USB charging specs etc. I'm only concerned at this stage with the suitability of these modules for supplying power.


Yes, that module should be fine for powering USB. Volts are volts and amps are amps. Things to think about:

  • Many small power supply modules have a minimum load, below which they may become unstable. The one you linked doesn't, but there is a note in the datasheet that noise may be worse at low loads, so if you can spare some current you might want to add a resistor across the outputs.
  • This particular module has a decent amount of ripple even at higher loads, so a filtering capacitor might be a good idea - I can't remember what the USB spec requires in terms of ripple.
  • A capacitor on the input might also be required, depending where you're powering it from.
  • \$\begingroup\$ Sounds reasonable to me. Do you know why point-of-load is explicitly mentioned then? It seems odd, that's all. It is just an "industry convention" thing now that multiple voltages are common? \$\endgroup\$
    – jfowkes
    Apr 19 '16 at 16:29
  • \$\begingroup\$ I always assumed that it was just a marketing thing. They are designed and optimised for that use. Some of them have minimum loads or restrictions on load capacitance which would make them poor general purpose supplies. \$\endgroup\$
    – Jack B
    Apr 20 '16 at 13:01

Yes they will work with any load within the output specs.

This module provides 5V at 3A, so it can power like 6 standard USB devices (up to 500mA) or a fast-charging (5V 1A) with a good headroom for future super-fast chargers :)


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