I found a need for a small and reliable boost circuit, to get to 5V from single cell batteries, up to around 2A output.
The design is fairly simple, using only 9 components in total:
You can freely clone the project and start making your own version using Altium’s CircuitMaker here (requires free signup, Windows only)
Quick Start Guide
- All pads labelled on the back of the PCB
- Connect your circuit ground to the “GND” pad
- Connect 1.8V to 5.5V to the “IN” pad
- Pull “EN” pad high. Pad is pulled low on the PCB assembly, so if disconnected the circuit defaults to disabled.
- Output 5V is provided on the “5V” pad, with reference to GND.
- Inputs/Outputs are not isolated.
This data was collected with a KA3005P power supply, and a small electronic load (MakerHawk Electronic Load Tester, but honestly this cheap (not very accurate) design is copied in a number of places).
Design Details and Notes
The PCB features 0.1″ holes for easy integration onto a standard bread board, and can also be soldered directly onto another PCB, as there are no components on the bottom.
Overall size of the PCB assembly is 16.7mm x 11mm, (comparable to a US dime) and the thickest part of the assembly (to top of the inductor) is 4.5mm.
- Output voltage is set to 5.15V, slightly higher than 5V. This is done so that at higher currents (1A and greater), the output voltage settles to 5.05V. In practice, 5.15V is safe for almost all components rated at 5V.
- The output voltage is set by R1 and R2. The equation is: Vout = (R1/R2 + 1) * 0.5. Hence if desired output voltage is 3.6V for example, R1 could be changed to 1333 Ohms (closest standard +/- 1% value is actually available as 1.33K, but that is not always the case). Again, in practice for your designs, you may want to target a slightly higher voltage of 3.7V.
- Quiescent current, when Enable (EN) is set low or not connected, is 240 nA. Even with a pair of AAA batteries, Quiescent current is low enough to enable a functionally indefinite lifetime.
- The Richtek IC provides several protection features (OTP, OCP, UVLO, Soft Start, etc), each of which help prevent damage to the circuit and downstream components.
- The IC switches at 500kHz, however above 1.95A output, an audible hiss becomes apparent. It is not very loud, but is noticeable.
- A good rule of thumb in your designs is to test and double check manufacturer ratings. Once you have your own data, add a further 10% safety margin to ensure good behavior. Hence, using the data in the graph above, remove 10% of the max rated current at each voltage to ensure startup behavior in almost all conditions.
- Cooling is not required under 1A output current, however above this point it is suggested. First to ensure the module doesn’t get dangerously hot, but also to avoid triggering the IC’s OTP.
- The circuit will continue to output 5V, even if input voltage reaches 5.5V. This makes the circuit resilient against minor voltage fluctuations.
- Keep in mind that this is a boost module, so input current will be larger than output current. For example at 3V input, max output is 5V at 0.75A, and efficiency is 58%. This means input current (which would be 1.25A at 100% efficiency) is 2.2A.
- In general, boost modules tend to have noisy outputs. This was not measured, but the datasheet provides expectation of ~40mV noise at 500kHz. If this is a problem in your application, likely a LDO regulator down to a lower usable voltage, along with more decoupling caps, is a good idea.
- The PCB does not use castellated holes, as they tend to increase manufacturing costs. This is also why the PCB is made thin, so that surface mount soldering can still be done to the exposed pads. If you really want castellated holes, the PCB can be cut with regular scissors to DIY make castellated holes. 🙂
- The IC is fairly robust to sudden dead shorts and over current conditions, however is unlikely to be bulletproof. One old school method to test power supply robustness is to attach the positive output to a metal file, and drag ground across the file. The rapid succession of short and open circuit will cause issues for most power supplies.
- Running multiple of these converters in parallel, to generate more output current, is not really recommended, as they do not have any of the features needed for this to work well (synchronizing switching frequencies, load sharing, feedback prevention, etc). Doing so might work for a small amount of time, but likely will be unstable under load and may even fry.