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By swinchen
#57327
Hi All,

I am designing a board that will be powered from a single-cell Li-Ion battery.

There are plenty of charger IC's out there, and the Step-Up/Step-Down regulator is easy....

What I am looking for is an IC that cuts off the battery if the voltage drops too low. I have been having a really hard time finding this. I know some Li-Ion batteries have this built in, but I can't find the chip anywhere.

I did find this little guy, but I can't read any part numbers.

If you have any suggestions or recommendations that would be great!

I almost forgot... it also needs to be soldered by hand. I found this guy but I do not believe I could solder that reliably without a stencil, and an oven.

Thanks,
Sam
User avatar
By leon_heller
#57328
I've soldered chips like that without any problems, using drag-soldering, even on home-made PCBs.

Leon
By AlexOtter
#57329
I've also soldered LGA chips like that without issue, using a homemade PCB and a small butane torch (or heatgun). You can tin the pads of the board and the leads of the chip with a regular soldering iron, then place them together and heat the board from the opposite side until the solder reflows.
User avatar
By leon_heller
#57330
An embossing heat gun works very well for solder paste. I still prefer a soldering iron, applying the solder paste is a bit fiddly.

Leon
By lyndon
#57332
Can't you just use a comparator (with hysteresis) driving a FET to turn the current on/off? Alternately, if you don't want to deal with all that analog design, an 8-pin AVR and a TTL-level FET will do the same thing with a bit of firmware.
By swinchen
#57333
lyndon wrote:Can't you just use a comparator (with hysteresis) driving a FET to turn the current on/off? Alternately, if you don't want to deal with all that analog design, an 8-pin AVR and a TTL-level FET will do the same thing with a bit of firmware.
The problem with the AVR solution is that it would always need to be running in order to determine when the voltage is back up to a safe level. Granted, the AVR is quite low power, but any drain on a depleted Li-Ion is bad for it.

I'm not terribly good with analog design, but with the comparator I am not sure how I would generate the supplies and reference voltages without leaving the regulator on... hrmm.
By RonnyM
#57337
The first pcb is only $1.95. Why wouldn't this work?
User avatar
By leon_heller
#57338
swinchen wrote:
lyndon wrote:Can't you just use a comparator (with hysteresis) driving a FET to turn the current on/off? Alternately, if you don't want to deal with all that analog design, an 8-pin AVR and a TTL-level FET will do the same thing with a bit of firmware.
The problem with the AVR solution is that it would always need to be running in order to determine when the voltage is back up to a safe level. Granted, the AVR is quite low power, but any drain on a depleted Li-Ion is bad for it.

I'm not terribly good with analog design, but with the comparator I am not sure how I would generate the supplies and reference voltages without leaving the regulator on... hrmm.
You could keep the MCU in sleep mode most of the time, just waking it up at intervals to measure the voltage. The power consumption will be negligible.

Leon
By swinchen
#57339
I think I will just go with the IC (the 2nd link in my first post) and try soldering it down. Still with the AVR I would need a known reference voltage. I know that could be as easy as a zener and a resistor... the chip seems "more elegant"
By theatrus
#57341
swinchen wrote:I think I will just go with the IC (the 2nd link in my first post) and try soldering it down. Still with the AVR I would need a known reference voltage. I know that could be as easy as a zener and a resistor... the chip seems "more elegant"
Without a PCB, I'd recommend doing it "dead bug" style. Flip it over, and solder wire leads to the pads. Its quite easy.

Otherwise, you can put solder balls on each pad, put it on the PCB, and heat (hot air, oven). Solder paste will work a bit better than just solder balls.