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I have a few step-up converter modules such as

supposedly based on the MT3608 IC:

There seem to be clones/identical ICs available, such as SX1308:

I am aiming for a battery operated (two alkaline cells, so 3..2 V input, 3.3 V output) circuit with an "off" current of around 1 µA. According to the datasheet, the EN pin set to 0 V (GND) should achieve exactly this - however, depending on input voltage and feedback resistor divider (= output voltage) setting, this varies between 0.1 to 0.2 mA, which corresponds to the quiescent current for the PFM mode of operation.

I'm testing at Vin=4.6V, Vout=10V, no load. Input current is approx. 1 mA when EN at Vin. With EN at 0V, Vout corresponds to Vin.

From that it seems the IC does go into shutdown, but simply fails to fulfill the specs?

Of course, the feedback voltage divider causes about 50uA at that input voltage, regardless of the IC's consumption, so it's probably not suitable anyway.

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  • \$\begingroup\$ Please post a schematic of what you are talking about. \$\endgroup\$
    – Andy aka
    Apr 14 '20 at 16:01
  • \$\begingroup\$ @Andyaka Sorry, I have no schematic of the module. I suspect it is identical to the one given in the datasheet. The module has the EN pin connected to Vin, so I cut that trace. \$\endgroup\$
    – handle
    Apr 14 '20 at 16:07
  • \$\begingroup\$ You need to find someone who is prepared to make a guess then. \$\endgroup\$
    – Andy aka
    Apr 14 '20 at 16:14
  • \$\begingroup\$ @Andyaka I am looking for someone with experience with this part. \$\endgroup\$
    – handle
    Apr 14 '20 at 18:15
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Not sure if you still care, but...

I think you'll find that the schematic for those modules is shown here: https://www.youtube.com/watch?v=zJJcdptSH80&t=151s

The datasheet states the FB pin leakage is 1-50nA, so you should be able to reduce the current through your resistor divider to e.g. 1uA.

It's possible that the MLCC are leaky; you can desolder them to check if they are increasing Iq during shutdown.

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  • \$\begingroup\$ Thanks, that video also was the topic of hackaday.com/2019/01/27/… (also see comments). The video's author states "... my version will reduce that current to about 60 micro amperes ..." (from transcript) and as such appears to confirm my findings. According to the schematic in the video, it has a larger inductor and smaller capacitors in comparison to the datasheet's "typical application". I've used a high-side MOSFET to switch power to my whole circuit including the boost module, resulting in negligible current when off. \$\endgroup\$
    – handle
    Mar 8 at 11:45

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