Re: Wave Bubble 2010
by rubidium on Wed Jan 08, 2014 7:21 pm
Here's what I think is the rationale for this option: The data sheet for the linear regulator IC1 specifies that minimum input voltage (pin1 of IC1) to that chip is the chip's output voltage (pin5 of IC1), i.e. 3.3V, plus the "dropout" voltage of the device (listed as 102mV typical). So for a stable 3.3V output needed for the MCU and other chips, one needs at least 3.4V at the input. Assuming something like a LiPo battery is used to power the Wave Bubble, then if pin2 of JP7 is bridged to pin1 and the LiPo drops below 3.4V, then IC1 will no longer be able to sustain supplying 3.3V to the MCU and other chips. However, if pin2 of JP7 is bridged to pin3, then the 5V boost converter, IC2, will instead feed the input to IC1. Being a boost converter, IC2 will continue to sustain its 5V output as the battery drains to exhaustion, and thus IC1 will continue to sustain its 3.3V output. That's why I run with pin2 of JP7 is bridged to pin3, and don't see any advantage to the alternative. Now if it were me, I would have simply used a boost converter arrangement for the 3.3V supply in the first place - but whatever.
Jim