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particle-iot / core

Hardware design files for the Spark Core, a tiny Wi-Fi development kit.
https://www.spark.io/
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Power regulator optimization #3

Closed zsup closed 11 years ago

zsup commented 11 years ago

Take another look at the power regulator circuit in detail to see if there may be opportunities to improve power performance within the space constraints.

satishgn commented 11 years ago

SPX3819M5-L-3-3 is a pin-pin compatible replacement part and economical too. http://www.digikey.com/product-detail/en/SPX3819M5-L-3-3

zsup commented 11 years ago

Yes but I'm not sure what we would gain here; looks like it has roughly the same specs as the current chip

Zach Supalla 312.953.3413 On Jun 27, 2013 2:59 AM, "Satish Nair" notifications@github.com wrote:

SPX3819M5-L-3-3 is a pin-pin compatible replacement part and economical too. http://www.digikey.com/product-detail/en/SPX3819M5-L-3-3

— Reply to this email directly or view it on GitHubhttps://github.com/sprk/core/issues/3#issuecomment-20102736 .

satishgn commented 11 years ago

I'm not sure/clear what is expected regarding the regulator. Are we aiming for more current, efficiency, replace LDO with buck/boost type?

zsup commented 11 years ago

The goal here is to be able to provide 500mA of consistent power consumption with a power source providing 3.7V to 5V (low end = lithium batteries, high end = USB power).

The problem with the current regulator is that, while it's spec'ed for 500mA, it has poor thermal performance. The nearly 1W of power dissipation needed to bring 5V down to 3.3V at 500mA would bring the die up to 200°C.

There are two options I've found so far:

zsup commented 11 years ago

Here's another option: http://octopart.com/mcp1825s-3302e%2Fdb-microchip-7342935

This one has the right specs, but it's pretty big. Might be able to fit it if we get rid of the tantalum capacitors though (ceramic capacitors will be fine with this part)

zsup commented 11 years ago

@satishgn — after looking around a bit, I think we should implement the MCP1825S-3302E: http://www.digikey.com/product-detail/en/MCP1825S-3302E%2FDB/MCP1825S-3302E%2FDB-ND/1636103

This part has the right current output, the right thermal performance, and the right dropout voltage. The only downside is that it's rather large.

I think, however, that the part can be fit by using 0603 ceramic capacitors instead of the big tantalum capacitors, and by eliminating the PTC resettable fuse, which I believe would no longer be necessary because this chip has internal current-limiting. Curious what you guys think about that.

Also, looking at the circuit that connects VCC to VDDA - does that capacitor need to be tantalum? If not, we have some further space savings (plus cost savings) by converting that to a ceramic capacitor.