Power Select HW Rev 2

Owned by Nita E
Dec 30, 2020
1 min read

Changes since last revision:

  • Since the board needed a “jump start” during validation, the board now contains a button cell battery for this purpose.

  • Modified layout to make soldering FETs easier (the area of the pour was too large last revision, which prevented solder from melting).

  • Changed size of fuse holders.

Schematic

How it works:

  1. While VBAT is not yet high, we have the 3 volt button cell providing power. The inverter is pulled low so that the load switch outputs 3 volts from the battery. This provides the 3v3 jump start that the board needs.

  2. Once VBAT starts to increase, it will pull the inverter high, which disables the load switch. This will cause the load switch to stop outputting 3 volts from the battery since it is no longer needed.

FW changes

The battery connects to PB1 through a series resister so that its voltage can be read. It would be nice to have an alert of some sort to change the battery once it drops to 2V.