Tested: MINI-360 (MP2307-based) “3A” Buck Converter Module

As mentioned in my earlier Canton-Power buck-boost module review, voltages from batteries are rarely exactly the voltages you need to safely and reliably power your electronic creations. While that converter was rather acceptable, the efficiency wasn’t exactly stellar. In the case your input voltage is always above the output voltage, it is possible to choose a buck converter module, which might be more efficient than a buck-boost converter as it only has a single converter stage.

As a result, I went looking for buck converter modules on eBay and it seems there is a lot of listings for a rather generic module with “MINI-360” written on the underside. It advertises being based on the MP2307 with 1-17V output, 4.75V-23V input, 1.8A current (3A maximum) and up to 96% conversion efficiency all for the princely sum of AU$1.00 each. I couldn’t resist having a few around just in case so I ordered a few.

Was this a wise decision or not? Lets find out.

The Module

The module itself, true to its word, is tiny – about the size of two thumbnails (quite literally). The module comprises only a limited selection of resistors, capacitors, a trimpot, an enclosed inductor and a Monolithic Power Solutions MP2307 3A, 23V, 340khz Synchronous Rectified Step-Down Converter IC. The module has four pads at the corners for input – in the picture, I have soldered header pins for ease of use.

The MP2307 chip claims to have an integrated MOSFET which can provide 3A continuously, over a 4.75V to 23V operating range. Outputs of 0.925V to 20V are available with up to 95% efficiency with cycle-by-cycle overcurrent protection and under-voltage lock-out. While the chip may be capable of this, it all depends on the design of the module and its supporting components as well. This may explain the confusing listings which claim outputs only up to 17V, or current ratings of 3A but only 1.8A continuous.

The unit uses a rather cheap open-frame trimpot to set the output voltage. Because of its size, I suspect it will be rather difficult to set and maintain an accurate output voltage as external influences such as shock, vibration, heating/cooling cycles, atmospheric contaminants and dirt affect the set resistance.

The underside is a completely flat plane with silkscreened indication of conversion direction and polarity. The module itself is not reverse polarity protected and according to the listing, is not short circuit protected although the chip does seem to offer it. With the exception of the “MINI-360” moniker, the module is otherwise anonymous.

From the side, we can see the module has a pretty small profile too, which makes it quite attractive for compact projects. Being such a simple module, it doesn’t seem like there is much that could go wrong.

Methodology

Testing methodology uses the same Keysight E36103A programmable power supply, B&K Precision Model 8600 DC Electronic Load and 4-wire sensing based breadboard set-up as used in the test of the Canton-Power module. The Panasonic 1000uF electrolytic capacitor to provide local input power decoupling is visible to the right.

Because the unit can output a variable voltage set by the trimpot, I decided to test it at a few commonly used output voltages – 1.8V, 2.5V, 3.3V, 5V and 12V. Input voltages used were 5V, 6V, 9V, 10.8V, 12V, 13.8V, 14.4V, 15V, 18V and 20V (upper limit due to power supply used).

Results

The first thing I tested as soon as I got it out of the anti-static bag was the quiescent current consumption.

At first, I thought I wasn’t reading my instruments correctly. Then, I thought I must have had a bad module, so I hurriedly unpacked another and soldered pins to it. Surprise surprise – they both were equivalently bad.

How bad? How about consuming up to 60mA just sitting idle depending on input/output voltage settings? Yikes. That’s like constantly running a “regular” Arduino board with no power saving at all. It’s not looking good, as this is going to affect the efficiency figures especially at low loads. Even looking at 12V to 5V, the quiescent is about 41mA which tells me you’re probably better off using a linear regulator if you’re only looking to power something small.

In light of that, it’s probably better stated as quiescent power. On this metric, we see the lower voltages being quite similar – 1.8V and 2.5V are below 0.4W quiescent, whereas 3.3V and 5V are around 0.5W quiescent for the most part. At 12V, the quiescent current approaches 0.9W, meaning that the module is likely to get noticeably hot just idling. As a result, while the chip might be capable of the voltage, maybe the module has been “undone” by poor inductor choice.

For 1.8V output, we see the efficiency lines are at best around 60% at 500mA load, but only 10% for a 20mA load. Above 500mA loading, the unit struggles to maintain a consistent output voltage and at 750mA, occasionally shuts down and restarts indicating overheat or overcurrent protection has kicked in. There are some “bumps” in the curve around the 12-15V region, as it seems the converter wasn’t too stable and the output voltage did seem to have “jumps”.

As the output voltage is set with the trimpot, I did my best over a long time to get the voltage dialled in as closely as possible. It was tough, as the backlash in the trimpot and effects of temperature and vibration caused the voltage to drift significantly. In testing, it seemed that the output voltage fell as the input voltage increased (except for 500mA). At higher loads, the output voltage was low at the low-end of the input voltage. Regulation is thus not particularly tight.

Increasing the output voltage to 2.5V sees slight improvements in efficiency, but still, peaking at shy of 70% under 500mA of load.

The trend of regulation issues at low input voltages and high load currents repeats, but now it seems that the output voltage increases as a function of the input voltage. While I did try my best to set a steady 2.5V, it proved to be nearly impossible by hand, so 2.55V was as good as I managed.

At 3.3V, the efficiency improves slightly yet again. This is a rather useful voltage – looking at the efficiency, for a 500mA load, around 70% efficiency is achieved, but at 20mA, it’s more like 10-20%. For a non-sleeping ESP8266 which might operate around 100mA, the efficiency is about 44% which isn’t great. A quick calculation seems to show that you’re better off with an LDO linear regulator going from 5V to 3.3V at even 250mA as it’s simpler and it’s going to be about 66% efficient. At 100mA, the input voltage would have to be 7.5V or above to “break even” with the losses in a linear regulator.

The trend of high-currents and low input voltages being an issue continues, but otherwise, the voltages seem fairly well maintained across a range of input voltages.

Moving up to 5V, it didn’t make sense to test the module with a 5V input as it would not be able to regulate at that level. As a result, testing started at 6V, even though it seemed that it probably didn’t regulate that well with such a small difference, resulting in (potentially) slightly inflated efficiencies. At lower input voltages, there is definitely a trend-up in the efficiency levels – in the case of 500mA, it’s within a stone’s throw of reaching 90%. But at higher voltages, it still doesn’t surpass 70% by much even at 500mA. At the low end of the load (20mA), efficiencies are still about 18% mostly.

I set the voltage as closely as possible, and I guess I didn’t do a bad job. However, it seems that having 6V input and expecting 5V out may be a bit too much to expect, hence there are visible regulation issues across all the input voltages. Otherwise, the trends remain fairly similar.

Finally, pushing all the way to 12V, the module does hit 90% efficiency, although at a point where regulation is probably not being enforced. At 500mA, the efficiency stays around 80% while at 20mA, the efficiency just scrapes past 20%.

Some significant voltage deviations are seen at various currents and this is suspected due to the increased heating when operating with output set to 12V.

As with the Canton-Power module, I did not look at the dynamic (changing load) performance, ripple and noise or thermal performance. However, I don’t think that’s entirely necessary given what is already presented above.

Conclusion

The MINI-360 is a cheap and small buck converter. But unfortunately, that’s where the good news ends. It seems to have quite a high quiescent consumption which affects its conversion efficiency quite severely, especially for light loads below 100mA, which makes using linear regulators potentially even more efficient in those circumstances or when the difference in voltage is small.

Other than that, at higher loads, the module output is unstable showing drifting voltage probably due to thermal effects on the trimpot combined with thermal effects on the chip’s internal MOSFET channel resistance.

During testing, it was shown that overheat/overcurrent protection seemed to be functional, as loads of 750mA or above in open-air caused the output to trip and cycle on-and-off, which is unfortunate, as the efficiency is higher at greater currents.

As a result, while it does work, it doesn’t quite live up to expectations on the 3A or 1.8A current delivery due to thermal limitations and is definitely not a power-efficient choice. This is not an indictment against the MP2307 as such, as other modules may perform better. This is probably because this particular module skimped on the inductor (high DC resistance or lossy inductance at the operating frequency perhaps) or has some flaw with the design or PCB, but I can’t recommend this module for use with battery-powered systems as it would mean wasting energy for no good reason.