SparkFun Forums

[ccool3]

Hi all -
I've been working on this project for a bit, and I'd appreciate some feedback on my design from some more knowledgeable minds. I built a prototype board, and have had a few issues so a new perspective would be helpful.

I've built a data logger on a bare-bones Arduino set-up. The data logger includes an ADXL345 accelerometer and a micro-SD card (both run on 3.3V). I would like to power the Atmega chip with 5V so that I can use the 16 MHz crystal. I would like to supply power to this set-up with a LiPo battery and include a circuit to charge the battery through a mini-USB.

I've chosen Microchip's MCP73833 (http://ww1.microchip.com/downloads/en/D ... 22005b.pdf) to charge the battery. To boost the battery voltage to 5V I selected the LT1302 (http://cds.linear.com/docs/Datasheet/lt1302.pdf). I then used a LDO regulator (http://ww1.microchip.com/downloads/en/D ... 22008d.pdf) to drop the 5V to 3.3V. I'm not sure if this is the most efficient design, so any tips in that area would be appreciated. I also added a switch so that I can charge the battery without supplying power to the other components. The goal of this would be to prevent data-logging while charging the board.

I've attached the schematic. Thanks for taking the time to look at it.

[waltr]

I'd suggest looking at the LTC3440 Buck-Boost regulator that provides 3.3V output from a single Li battery. This would be much more efficient than boosting to 5V then regulating back down to 3.3V.

[ccool3]

Thank you for the suggestion, but I do not think that the LTC3440 solves my need for 2 voltage outputs: 5V & 3.3V. I would like to supply 5V for the Atmega chip so that I can still use a 16MHz crystal. I also need a 3.3V supply for my other sensors. My understanding is that if the Atmega is supplied 3.3V then only an 8MHz crystal can be used, and I would like to keep the timing accuracy of the 16MHz crystal.

[waltr]

Ah, got it. I didn't realize you needed 5V.
If you do need more efficiency then maybe a 5V boost converter and the 3.3V buck-boost converter would be a help. This would depend on how much current is needed at 3.3V.

[ohararp]

cccool3, I'd take a look at microchips MCP1252 chips. You can get them in in 3.3V,5V and adj formats. I use this in my dataloggers all the time. You are limited to 120mA but they should work fine for this app. Otherwise I recommend the TPS6300X units.

[ccool3]

Thank you for the suggestions. I'll take a look at them and see what will work out best.