2
\$\begingroup\$

I am not pretending to use this, but as a general curiosity, when the AT32UC3C2512C datasheet says in page 1259, Table 40-20, parameter Iout, that the internal 3.3V regulator has a 35mA DC output current, does it mean I can actually use it as a power source, as long as I don't use more then 35mA out of it?

EDIT:

As requested:

Table

\$\endgroup\$
  • 1
    \$\begingroup\$ It does sound that way but i've not read the data sheet. Maybe you can create a picture of that page and table and post it. Purely for lazy people like me. \$\endgroup\$ – Andy aka Sep 1 '13 at 22:02
  • \$\begingroup\$ I'd avoid it, simply because any ripple on that regulator's output could cause all sorts of mess if it's designed to be some kind of internal reference. The price and additional complexity of adding a separate 35mA rated 3.3V voltreg is so small that it barely compares to the potential cost and effort of dealing with bizarre glitches once you hit production. \$\endgroup\$ – Polynomial Sep 1 '13 at 22:41
  • \$\begingroup\$ @Andyaka as requested... \$\endgroup\$ – mFeinstein Sep 1 '13 at 22:44
2
\$\begingroup\$

I think pg. 88 and the info/diagrams on pages 46 onward answer your question quite well:

8.5.9 Voltage Regulators The embedded 1.8V regulator provides the core supply. The embedded 3.3V voltage regulator is used to supply the USB pads. Both regulators are turned on at startup. If the application is supplied with a voltage range around 3.3V or the application does not use the USB interface, the 3.3V voltage regulator has to be turned off by writing 11 binary to VREGCTRL.VREG33CTL. The 1.8V voltage regulator has its own voltage reference that is calibrated through the VREGCR.CALIB field. This field is loaded after a Power On Reset with default values stored in factory-programmed flash fuses. Although it is not recommended, it is still possible to override the default factory settings by writing to those registers. To prevent unexpected writes due to software bugs, write access to this register is protected by a locking mechanism, for details please refer to the UNLOCK register description.

enter image description here

So essentially it's not meant for use supplying external components, rather so you can add decoupling if it is being used. To add a pin for decoupling like this is very common (since large value caps are not feasible on the die)

\$\endgroup\$
  • \$\begingroup\$ That was my impression too, but since its not explicit I rather to ask. \$\endgroup\$ – mFeinstein Sep 2 '13 at 16:44
  • \$\begingroup\$ Speaking about the decoupling, the recommended diagram appears to be bad practice, they suggest 2 decoupling capacitors for 5 pins, and most of them spread around the IC... \$\endgroup\$ – mFeinstein Sep 2 '13 at 16:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.