Li-ion protection modifying - Page 1
Forum section: electronics / projects

author: bodzio_stawski
author_rank: Regular Contributor
timestamp: January 27, 2021, 06:10:47 pm
content: Hello!I have a li-ion protection IC - AP9101CK6-AXTRG1 to connect with n-type MOSFETS. And this one has the overdischargedetection voltage at 2.8 V.https://www.tme.eu/Document/2363835cc5634a92b6e94bc773e39f4b/AP9101C.pdfTypical aplication looks very similar to the other protection ICs (like DW-01).But I wonder if there is a possibility to modify/adapt such a schematic toincreasethe voltage limit (eg to 3.3V). Is it possible in such circuits?

author: jbb
author_rank: Super Contributor
timestamp: January 27, 2021, 07:23:07 pm
content: You could perhaps try a voltage divider, BUT that would change the over voltage threshold too. I don’t recommend it.Safest solution is to source a different version of the chip with higher setting built in.Practical solution is to apply some under voltage sensing in your circuitry to go to sleep when the voltage gets low.

author: bodzio_stawski
author_rank: Regular Contributor
timestamp: January 27, 2021, 08:22:33 pm
content: Yes, right:), for a moment I considered a voltage divider or a diode between R1 and Vdd, but that's a rather bad idea:(Another chip with higher voltage setting will be my dream, but 3V is the maximum which I see for some ICs :cQuoteCould you write an example?

author: jbb
author_rank: Super Contributor
timestamp: January 27, 2021, 10:54:50 pm
content: Well, maybe you could use a soft power switch circuit, and put a voltage supervisor chip down to turn it off if voltage goes low.If using a microcontroller, you could use low power sleep modes.Some have a Brown Out Detector to reset the chip. On boot up, you can look for a BOR status bit; if set, you know something went wrong and can go to deepest sleep mode.Alternatively you could use an ADC to sense the battery voltage every once in a while and go to deepest sleep if it’s too low. (But make sure the battery voltage measurement circuit doesn’t waste too much current...)

author: bodzio_stawski
author_rank: Regular Contributor
timestamp: January 28, 2021, 09:11:36 am
content: Thank you for the reply:)Unfortunately I have to deal with the undervoltage protection without any microcontroller:cBut I'm interested in voltage supervisor chip and I have to check it.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 28, 2021, 05:14:44 pm
content: The solution suggested by jbb is better.Battery's protection should just be that - to protect the battery.I take it that your circuit is not guaranteed to operate properly under 3.3V, thus you want to switch off the power supply if so.First thing to do is: make sure this is really needed. Take a close look at your circuit's design and at the ICs datasheets. Except if you're using the 3.3V rail as a voltage ref. for ADCs, for instance, then getting as low as ~2.9V may not be a problem. It usually isn't. Most modern 3.3V MCUs can run at 2.9V.If this is still a real problem, then using a voltage supervisor of some sort would be best. A "graceful shutdown" of the system may also be a better option than just switching off the power abruptly. So you could use the supervisor's output at the software level to decide what to do and possibly force the shutdown programmatically, or put the MCU in standby, or anything else appropriate. Say, as suggested above, that the 3.3V rail serves as a voltage reference of some kind. If this rail falls under 3.3V, you could decide to stop doing whatever needs this reference, and do everything else. That may make sense from a system's (/user's) point of view.Just some food for thought.

author: tooki
author_rank: Super Contributor
timestamp: January 29, 2021, 09:37:20 am
content: Quote from: bodzio_stawski on January 27, 2021, 08:22:33 pmWhy not just use the ANTRG1 version, whose discharge cutoff is 3.2V? (It looks like that version is one designed to be gentle on the battery, since its discharge cutoff is high and its charge cutoff is sliightly low.)

author: bodzio_stawski
author_rank: Regular Contributor
timestamp: February 04, 2021, 08:07:30 pm
content: Yes, I considered using ANTRG, but because of unavailability in my country I refused to use it at the beginning. But if it is worth money, I really have to get it. Thanks to all for advices!:)