MP3437 boost converter IC - Vdd pin voltage

[newtekuser]

I was planning to use the MP3437 IC to boost 5v to 12v, but I see the VDD pin takes 3.6V max. Can I drop the 5V to 3.6V using a resistor divider for this pin, or do I need regulated 3.6V to the Vdd pin?

https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP3437/document_id/6889/

[Ian.M]

Its got an internal regulator for Vdd.  For 5V in operation, simply connect the required decoupling cap to that pin and *nothing* else.

[newtekuser]

Its got an internal regulator for Vdd.  For 5V in operation, simply connect the required decoupling cap to that pin and *nothing* else.

On page 17 of the datasheet it says external power source for Vdd should be limited to 3.6V, this is what confuses me. Likely I’m not understanding something.

[Ian.M]

External power to Vdd is needed when running from single cell alkaline or NiMH batteries, energy harvesting applications and similar very low Vin.  If you feed Vdd with a 3.5V external supply, the internal regulator is disabled and the converter will start with Vin as low as 0.95V and run down to 0.8V, or feed it 3V and let the internal regulator take over, powering Vdd from the output once running.  That leaves you with the problem of getting 3V or 3.5V from 0.95V Vin, but as only a couple of mA will be needed, that's not too tricky.

As you've got 5V Vin, (or at least 4.4V USB Vbus), you don't need to bother with any of that.

[newtekuser]

External power to Vdd is needed when running from single cell alkaline or NiMH batteries, energy harvesting applications and similar very low Vin.  If you feed Vdd with a 3.5V external supply, the internal regulator is disabled and the converter will start with Vin as low as 0.95V and run down to 0.8V, or feed it 3V and let the internal regulator take over, powering Vdd from the output once running.  That leaves you with the problem of getting 3V or 3.5V from 0.95V Vin, but as only a couple of mA will be needed, that's not too tricky.

As you've got 5V Vin, (or at least 4.4V USB Vbus), you don't need to bother with any of that.

I see, thank you for clarifying this! I see this too in the first example schematic on page 1 where Vdd is tied to ground via using a 4.7uF cap. However, if I do this, DRC complains about input power pin is not driven by any output power pin.
Safe to ignore this error I suppose in this case?

[Ian.M]

Yes, that's a bogus DRC warning.  If your EDA package permits, the pin should be flagged as optional power, if not it shouldn't be flagged as a power pin.