Background

VKLSVAN DC-DC converter works more than 2V input. Is it capable of 3.3V output for MPU?

Summary

It doesn't start at 2V but 2.5V. Without additional capacitor, it works like PFM. With 10uF capacitor, output noise voltage decreased well. The noise is the same as swiching power supply.

経緯

3.3V 電源の MPU を乾電池駆動したい。

要約

2本のマンガン単1電池により 3.3V 100mA 出力を確認した。

Specifications

Input Voltage: DC 2V-24V
Output Voltage: DC 5V-28V (Recommended within 26V)
Peak Current: 2A (1A is recommended for a long time)
Max Coversion Efficiency: 93%
Max Load Power: 7W
Board Size: 30 X 17 X 6.5mm
Pin Definition: Input to IN-IN + / Output to OUT-OUT +

Note: This is a boost converter module, so the output voltage should be at least 2V higher than the input voltage.

Task

Is it applicable for battery driven Arduino power supply?

Method

Enoki used self made power supply for the DC-DC input supply.

The self made supply was supplied by DM-310MV (15V 10A).

DSO SDS1102 CH1 [1V/div] and CH2 monitored input and output voltage of the target by DSO measurement. Output noise voltage was measured by DSO measurement peak to peak.

Photo1 shows the measurement.

Photo1 VKLSVAN

The result

Figure1 shows the result.

Figure1 Ripple/Noise output voltage

Fixing output voltage 3.3V, 3V was necessary for stable output. 3V is too high to drive by 2 1.5V batteries. The peak-to-peak noise voltage varied 37 to 99 kHz like PFM.

Looking for the DC-DC IC specifications, it seems to be MT3608 alike.

The APPLICATION INFORMATION recommends to add 22uF ceramic capacitor to output.

So Enoki added 10uF ceramic capacitor as shown in Photo2. It worked at 2.5V input.

Photo2 VKLSVAN with 10uF

But it stopped step-up when loading 324 mA as shown in Figure2. The interval frequency was 1.2 kHz.

Figure2 Excess load stops converting

2 D batteries driven

Enoki tried 2 Mn D (R20) batteries for input as shown in photo3.

Photo3 VKLSVAN driven by batteries

Increasing output to 5 12 33 67 100 mA, output voltage was constant 3.35V. But input voltage dropped to 3.23 3.21 3.19 3.16 3.10V.

Enoki bought the new batteries on 2021-04-16 at Daiso. Although the batteries reservation date is 04-2023, they lighted dark when applying for flash light.

Conclusion

Enoki confirmed that the VKLSVAN DC-DC can step up 2.5 to 3.3V for 100 mA range within 150 mVpp noise. The VKLSVAN note is meaning less.

It seems that input batteries voltage dropped because of internal resistance.