TicTocTrac

Unfortunately, the boost converter that met the needs of our project is only manufactured in a QFN (Quad Flat No-leads) package. These devices are impossibly tiny and are normally soldered via machine, so we’ve put together some instructions based on our experience (and our 4 dead boards).

1. You can show pin numbers in eagle by going to options -> set then misc then check “display pad names.”


2. NOTE: The UVLO circuit currently cuts off at too high of a voltage to be useful. To fix this do the following: Don’t populate C2 (it probably doesn’t hurt...but isn’t necessary) and most importantly change R3 from 2MOhm to 1.2MOhm.


3. Cut the trace on the bottom of the board going between pins 6 and 8 of the boost converter.


4. Put down a thin line of solder paste along the pads of each side on the board.


Tip: You can keep your solder paste good longer if you DON’T use the little tip that comes with it. Instead squeeze out a bit on a piece of paper and use a toothpick to apply the paste. Then replace the cap.


5. Use a toothpick or razor blade to scrape solder paste out from between the tabs.


NOTE: Only put a very thin layer of solder paste down at this point.


6. Put a thin layer of flux on the bottom of the boost converter.


7. Position the boost converter down appropriately.


Pin 1 is marked by a circle on the package and a line on the board.


8. Hold the chip down lightly while you hit each pin individually with the soldering iron.


9. Now put down another thin line of solder paste on each side touching both the pads and the side of the boost converter. Run your soldering iron smoothly down the sides of the package.


10. Cut open a stranded wire. Use a single strand to jumper pin 9 to ground (one side of R4 works well for this).

TESTING (NOTE: don’t try to touch the pads, find bigger components that are connected to them to use as test points)

1. Check for shorts both visually and with the multimeter.


2. Check for short between power and ground.


3. Apply 3.3 or 5 volts at Vbatt.


4. Check that Vcc output is reasonable - usually about 3.27V.


5. Check that Vaux (pin 1) charges to a reasonable value (usually close to Vbatt).


6. Check that UVLO (pin 7) is reasonable - usually about 0.33V.


7. Check that Vfb (pin 10) is reasonable - usually about 0.55V.

Enjoy your shiny new boost converter that doesn’t output 6V or burn your finger off!

Even when cautions, it’s highly likely you will short the Lithium-Polymer battery at some point. The most common symptoms are a very hot boost converter and finding that the battery is producing little or almost no voltage on the other side of the protection circuit while the battery is charged. If you are using the Sparkfun 110mA LiPo, there is an easy way to reset the protection circuit. This technique isn’t guaranteed, but has saved our LiPo 9 out of 10 times.

1. Quickly remove the offending short (if visible) and disconnect the battery fully from the board. While we have seen the boost converter survive some very hot temperatures, time is essential for saving the SD card. Shorts most commonly result from accidentally letting the battery leads touch while soldering them to the back board, shorting the leads with wire-cutters while trying to trim them after they are soldered to the back board, and flecks of solder paste landing in the least opportune locations.

2. Remove the Kapton tape from the battery. Unfold the protection circuit and remove the masking tape covering the leads. You can now test the voltage directly off the battery and compare it to the voltage on the other side of the protection circuit.

3. Fully desolder the positive lead of the battery from the protection circuit. This should reset the circuit.

4. Resolder the lead back to the protection circuit.

5. Test for a voltage on the other side of the protection circuit. If you have a voltage – congratulations! Your battery has been revived! If not, you can try disconnecting the battery from the protection circuit again, but its protection circuit may have died.

We made our adaptor to connect the male board-to-board connector on the top board to the ISP from a female board-to-board connector soldered to a ribbon cable with a male 2x3 connector with the same pitch as our ISP on the end.

We primarily used a Bus Pirate as our main programmer. If you are using an AVR ISP mkII you will need to make a small modification to the ISP to provide power to the board from the ISP. We chose to simply power the board from the 5V line when programming even though the board is designed for 3.3V. This is reasonably safe when the board is connected to the ISP for short periods of times and we have encountered no problems with this method. (Note: To use this method successfully, the top board must be plugged into the modified AVR ISP before powering the ISP.)