Custom step-up circuit?!

Community PCB Design
1

Hey guys I hope I can get some advice here:

I need to design a custom step-up for my project.

I will be using a Li-ion battery pack, 3.7V at 1400mAH. I need to step it up to 5 - 5.5 volts, running up to 5A. It will never exceed or be a steady 5A.

I have looked for tutorials or design examples but can’t seem to find anything sufficient.

*I well be designing this into my existing micro design in Eagle

Any help is greatly appreciated!

2

Actually I am trying to mimic Sparkfuns Power Cell - LiPo Charger/Booster, except running “not charging” at 5V @ 5A max

3

Here’s one approach:

Take a look at:

http://parametric.linear.com/external_p … t_5!iout_5

Choose an IC based on availability and package type, ie. what can you get hold of, and what can you easily solder to your PCB.

Then download LTSpice IV:

http://www.linear.com/designtools/software/#LTspice

…which is a fantastic tool IMHO. It includes example circuits for a huge range of Linear Tech components, including switched-mode power supply controllers. You should be able to customise the example circuit to represent your design and to see the effect of any changes. You can use it to check efficiency, stability, accuracy and noise.

4

VERY COOL! Thank you, now what about over discharging the battery? Is there a component that will make sure the battery wont over discharge below the threshold? So if I can get away with not having to make a step-up will I still need a circuit that will protect the battery from over discharging?

5

Do you know for a fact that your 1400mAH battery can handle 7A+ output current without tripping the current limit?

6

macegr:
Do you know for a fact that your 1400mAH battery can handle 7A+ output current without tripping the current limit?

If it’s a LiPo intended for model aircraft use, it will be fine. Most batteries are rated at well over 20C discharge current (i.e., 28A for a 1400mAh battery), and some as high as 90C peak current. Of course, it will go flat pretty quick at these discharge rates!
7

bamboosamurai:
VERY COOL! Thank you, now what about over discharging the battery? Is there a component that will make sure the battery wont over discharge below the threshold? So if I can get away with not having to make a step-up will I still need a circuit that will protect the battery from over discharging?

Some switchmode regulators have an “undervoltage lockout” feature built in you should be able to use, but if not you can implement it pretty easily with a comparator whose output is connected to the “enable” line on the regulator. Or you could use a dedicated LiPo protection chip which does undervoltage protection.