SparkFun Forums

[thankyou]

I want to use a cheap 3.3V regulator in my project that uses an LIR2450 3.6V lithium ion coin cell battery. I noticed there are many buck/boost +3.3V switching regulators specifically for lithium ion batteries. I would prefer using an LDO linear 3.3V regulator for the lower cost and not having to use many external components. Is there a problem with using this type of regulator with a lithium ion battery? There might be another issue in the dropout voltage being too high. I'm not sure how long it would take for the LIR2450 to get below 3.6V (I found a regulator with a 0.3V dropout). Just wondering if you can give advice about this before I order parts and do testing...thanks!

[jremington]

Why do you want to use a regulator?
Most coin cell powered projects do not use one, so tell us what you really want to do.

[thankyou]

I need the supply voltage to be stable at the same value while the application is running. This is because I'm comparing analog input voltages (that are based off of the supply voltage) to threshold voltage values in the microcontroller, so I don't want the input voltages to change if the battery voltage fluctuates.

[jremington]

It would be much better to use another voltage reference than the supply.

[thankyou]

How would you use a voltage reference that doesn't come from the supply? I don't want a second voltage supply.

Also, I read that you shouldn't use the lithium ion LIR2450 below 2.75V. How would you cut off the voltage?

[jremington]

I would use a voltage reference that derives its power from the supply. There are plenty of 2 and 3 terminal external references, in a wide range of voltages, that are cheap and extremely accurate. Also, most micros have a built in, stable voltage reference (although not necessarily accurate, so they need to be calibrated).

It is essential to use a low voltage cutoff with any Li-based battery, or it will be destroyed in a single usage. Those batteries are also quickly destroyed by overcharging, so you also need special charge controllers. There are a number of cheap, lithium battery protective circuits available. Google "battery protection pcb" for some examples.

[thankyou]

I'm using an Attiny84 that has an internal 1.1V voltage reference, so I can't power a circuit that requires 3V. Why would a voltage reference be better than using a voltage regulator? I looked up voltage references and it looks like it would either be a Zener diode or a "bandgap" voltage reference. The Zener diode has a higher voltage requirement and limited output voltages so that doesn't look like a good option. I'm still trying to find a bandgap reference that has a high enough output. The charger I'm using for the LIR2450 is this: https://www.sparkfun.com/products/10401. Now I'm trying to find an "undervoltage lockout" IC for the lithium ion battery to shut off when it's discharged too much. If only there was an IC that had both a voltage reference output and undervoltage lockout...

[thankyou]

I think I found the best solution:
http://www.st.com/st-web-ui/static/acti ... 085223.pdf

It's a lithium ion battery charger that incorporates an LDO 3.1V regulator with battery protection circuitry, including over-discharge.