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I'm working on a LiPo charging design with the intention of producing several 1000 of them. There needs to be a switch to turn the charging function on and off. To me, it seems to overcomplicate the design and manufacturing process to have to program a microcontroller just to handle the on/off functions. I would like it to have a 3-second delay to turn on and a 3-second delay to turn off, SOME kind of delay. Do pushbutton controllers exist for this purpose?

What is the better option given that I intend to produce 1000s of these?

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  • \$\begingroup\$ Are you willing to pay for thousands of pushbutton controllers? Or would you rather use an MCU you probably already need to have anyways? \$\endgroup\$
    – DKNguyen
    Feb 28 '20 at 16:21
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    \$\begingroup\$ Why do you need the delay? I'm sitting imaging I've bought your gadget, and turn it on. Why do I have to wait three seconds for it to turn on after I push the button? \$\endgroup\$
    – JRE
    Feb 28 '20 at 16:33
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    \$\begingroup\$ What are you you using for charging control? Is that already based around a microcontroller, or a dedicated chip? \$\endgroup\$
    – Phil G
    Feb 28 '20 at 16:35
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    \$\begingroup\$ @LucaDaidone $5 a pop on Digikey? That feels wrong \$\endgroup\$
    – DKNguyen
    Feb 28 '20 at 16:51
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    \$\begingroup\$ Such chips exist. An MCU might be cheaper but it's your job to evaluate the options. \$\endgroup\$ Feb 28 '20 at 18:27
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"Soft latch circuit", "soft latch power switch", or "pushbutton controller" are the keywords for searching for circuits like this. You can find tens of IC's that do this sort of thing by googling "soft latch power switch IC"; many have programmable delays.

I hate to recommend specific parts (cause shopping and buying recommendations are off-topic for this site), but I'll recommend STM660{0,1} and TPS342{0,1,2}. They're both parts I've used for similar purposes.

What is the better option given that I intend to produce 1000s of these?

It's a tradeoff between cost, off-state power consumption, and manufacturing difficulty. You can get an ultra-cheap microcontroller (some manufacturers in Taiwan and China have $0.03 offerings), but it will take more power when the system is off and will add manufacturing and design complexity: now you have another chip that needs to be programmed when you manufacture the widget and another binary file to keep track of. Generally, the specialized "pushbutton controller" chips will cost more (I realize that this is counter-intuitive, but I think it's because they are less general-purpose than an MCU and therefore have a smaller market), but will simplify design and manufacture and will be more efficient.

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  • \$\begingroup\$ I would add LTC2950/LTC2951 and MAX16054 to the list. There are so many choices it is strange to even ask this question. BTW, the search for "pushbutton controller" will get you there faster than "soft latch". \$\endgroup\$
    – Maple
    Feb 28 '20 at 18:09

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