Electronic – USB2 powering 3.3V at 500 mA

3.3vldousb

I have the above simple requirement, and I'm frankly astonished that I can't find it as a simple chip.

My understandings:

  1. USB2 provides 5V on its power pins;
  2. USB2 assumes 100mA, but will provide 500mA upon negotiation;
  3. Most USB2 sources just provide 500mA anyway – but I want to be "official" and negotiate for it first;
  4. USB3 does "power delivery", but those chips are SO complex that they're overkill for my situation.

I have a 500mA, 3.3V circuit (330mA @ 5V) that I'd like to power from 5V USB. So I'm looking for a simple chip that has 4 USB pins (I assume the Data pins are part of the negotiation!) and one 3.3V output pin that can supply 500 mA – noting that ~750mA is the theoretical maximum. If there needs to be a couple of extra pins for support components (capacitors, inductors, etc.) then so be it, but I'd hope there wouldn't be many.

I've found all sorts of devices for USB chargers (on the "host" side – no good), USB Hub controllers (to even out multiple ports' requirements – too complex), USB peripherals with incidental output voltage (e.g. FTDI – way too complex), and even one 8-pin device that's almost ideal – but it stops at 200mA (300mA @ 3.3V).

Why isn't there a device that negotiates for 500mA, and then simply delivers it at 3.3V @ 750 mA (or close)?

Best Answer

Mostly because of the impractical need for one. As you mention no one really cared about the usb power enumeration so it has been defacto ignored. And it never worked with usb power supplies. Plus you would need active circuitry to do so. For a power only non data transfer device, its an added expense with little benefit. Usb requires constant data transfers or a keep alive message. Usb requires you to enumerate as a device on the host. Enumerating as an unknown device would lead to messages on the computer about it.

You can roll your own if you really wanted to. Take a 5v to 3.3V switching regulator with an enable pin and take a usb capable microcontroller like an attiny based v-usb or real usb atmegaU and program it as a usb serial device. Once enumerated you can switch on the regulator for your output. Bonus serial connection if you need it. Not a single chip solution but with two modules off fleabay and 20 minutes of setup you can have what you want.

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