Introduction: Power Management for CR2032
Doing low energy application needs some special complnents and code-lines care. Some components give this feature, some other need to be worked on in short time. the main idea when we work in very low energy application is the type of battery. the choice of this depends on :
- The size of the application (mechanical part)
- The quantity of energy needed (parameter in mAh)
- The area's temperature (temperature has influence in some types of batteries)
- The power consumption (energy consumpted by the dispositive)
- power capability (In demand current, how much battery can give in Amper)
- tension area of component 's work (voltage needed to activate electronic component).
Between all these characters already mentioned The most important That should be taken in consideration is the voltage of every component.So when the Energy drops and the energy of the battery drops up, We have to be sure that all component work and respond.
for example if we use the battery CR2032. the capacity of battery is 230 mAh and the voltage is 3V and supposed to be in low state and have to be changed when the voltage drops down to 2 volt. then we use NRF24L01+ ,ATMEGA328P and DHT11 to make a wireless temprature unit. The processus can work normally with NRF2401+ and atmega328p(with 4Mhz frequency) because it can work from 1.9 voltage. but for DHT11. if the battery drops under 3 volt, the sensor won't be not stable and we get wrong data.
in this instructable WE ARE GOING TO PROPOSE A VERY LOW ENERGY REGULATOR for battery CR2032 that can handle the output into 3 volt as the input is low as 0.9volt. we go to use
Step 1: The Main IC
We are going to use TPS6122x from texas instrument. it provides regulated power-supply solution for products powered by either a single-cell, two-cell, or three-cell alkaline, NiCd or NiMH, or one-cell Li-Ion or Li-polymer battery. it operates by input voltage from 0.7 to 5.5 v and gives stable output voltage. it exists 3 versions :
- TPS61220 : adjustable version, you can fix the Output Voltage from 1.8 V to 6 V
- TPS61221 : 3.3V fixed output, used in this instructable.
- TPS61222 : 5.0V fixed voltage
it has good efficiency with low quiescent current : 0.5 μA. and low consumption current in shut down state : 0.5 μA.
it is a good choice for a long life-time and can assure a voltage stability.
Step 2: Schematic and Make It Alive
The schematic exists in official datasheet. some details need to be taken as noticed. the inductor L and the two capacitors need to be in good quality. When doing PCB, we need to make the capacitor and inductor close to the chip. we add the battery holder, and we made the input pulled up using high resistor value. so you can shut down the ic by just pulling down the enable pin and the big value of resistor let the current very low.
I designed the schematic using eagle cad and I made this solution as module for testing and prototyping. I added a CR2032 battery holder, and I made PINOUTS like this :
- GND : ground
- ENABLE : activate / desacativate the regulator
- Vout : the output regulated to 3.3V
- VBAT : the out of battery directly, you can use another source as input for this module (make sure that any battery is installed)
Step 3: Make It Alive
the main ic used in this project is very small, so making it in breadboard for test is not easy, so the idea is to make a pcb that handle all the schematic, and we add some pinout functions like enable, disable, access to the input if we want to use other battery type.
I share with you the schematic in EAGLE CAD Link
GND : commun ground
ENABLE : the module work directly if this pin is not connected or connected to high level, when pulled down the regulator stops working and the output is connected to input or battery
VOUT : the regulated output voltage
VBAT : it can be used as an input if you want to use another source, you can read directly the voltage of equiped battery
Step 4: Test
Board finished and made by makerfabs, I maked video how is work