[onerng talk] *****SPAM***** BOM Information

[Gerd v. Egidy]

> What's with the AP3105 20V source. They don't make the AP3105 it in a
> SOT-23-5 package.
> 
> Is that actually some kind of switching/linear reg of different part number?

The AP3105 is a pwm controller designed for ac/dc flyback regulators - that 
doesn't make sense here.

Most probably it is a typo and the AP3015 is meant: that is a dc/dc step-up in 
SOT23-5.

When looking at the schematic I see a problem with it's use though: The 
shutdown pin is tied to 3V3. That means the regulator starts as soon as the 
onerng is connected to usb and gets power. The AP3015 will draw 350mA during 
startup to bring the 1 µF cap up to 20V.

That is not allowed by the usb spec.

You are only allowed to draw a max of 100mA until the usb device is enumerated 
and the host controller actively grants the higer power. You should have 
connected the shutdown pin to the CC2531 (and a pulldown resistor) and only 
activate it when the usb is successfully enumerated. Also when the device is 
suspended by the usb bus, you are only allowed to draw 2.5mA, which you'll 
probably blow with the active stepup. So another reason to make it switchable.

This setup will probably still work on most computers. But it is not good 
design.

I'd switch to the AP3015/A which is limited to 100mA input, that should be 
well enough for this circuit. Since you'll charge up the input capacitors at 
the same time, you'll most probably still violate the 100mA spec. But not as 
bad as with the AP3015.

Kind regards,

Gerd