Li-Ion Battery UVP protection circuit - Page 1
Forum section: electronics / projects

author: alinp
author_rank: Newbie
timestamp: January 25, 2018, 04:20:06 pm
content: Hi,Given one Li-Ion cell (18650 for example) I have tried to design a circuit that cuts off the power when the cell reaches 3.3V. Simple right? Yeah, so I thought...At first I had a look atTVL3012reference design in the datasheet (pag.8 Battery Level Detect) and taught about using it along with a P-Channel MOSFET to do so. The problem is that without a hysteresis it oscillates back and forth, due to the battery voltage rising up once the load disconnects.After that I had a look at anAsymmetrical Inverted Schmitt Triggercircuit, which would allow me to set the ON/OFF thresholds to 3.3V (load disconnected) and 3.5V (load once again connected). The problem with this one is that the battery being the only power source in the system I cannot have a reference for my Schmitt trigger circuit. One solution to this would be to step-up the battery voltage and then regulate it to a reference voltage of, let's say, 5V. Neah, this doesn't work either. This entire protection circuit would need to have current consumption of <5uA.So, any idea on a circuit that:- disconnects a single cell Li-Ion battery at 3.3V- reconnects it back once the battery gets charged at 3.5V- has a current consumption of less than <5uA?Btw. the charging circuit that i plan to use is a BQ24040. Unfortunately the UVP (Under Voltage Protection) on this one is 2.8V at max. I need at least 3.3V.Any help or idea is greatly appreciated!

author: Gribo
author_rank: Frequent Contributor
timestamp: January 25, 2018, 05:51:19 pm
content: The Ablic (formerly Seiko) S8240 supports up to 3.4V with 1.5uA consumption.https://www.ablicinc.com/en/doc/datasheet/battery_protection/S8240B_E.pdfEdit: It seems you will have to ask them regarding voltages not specified in the data sheet.

author: alinp
author_rank: Newbie
timestamp: January 25, 2018, 06:20:33 pm
content: I've also found S8240 while searching for an IC to accomplish the task, more specifically the S-8240ABO-I6T1U model. Unfortunately this model (and many of the models produced by ABLIC) aren't available at local suppliers like Farnell, Mouser or TME.Later edit:Many of their configurations can be found in thisdatasheet. Even DigiKey doesn't have the S-8240ABO-I6T1U model. Furthermore, I know nothing about this manufacturer.Any other suggestions?

author: Gribo
author_rank: Frequent Contributor
timestamp: January 25, 2018, 07:07:44 pm
content: You can use a MAX809 for the voltage level detection, there are variants from 2.3 to 4.8V and it is available from several different manufacturers (Maxim, Onsemi, ST, and TI). Its current consumption might be slightly higher than your limit though.

author: alinp
author_rank: Newbie
timestamp: January 26, 2018, 08:32:17 am
content: Regarding MAX809, I might be wrong, but:1. I haven't seen any model with a 3.3V threshold value (VTH)2. It has no hysteresis; it rather implements a timeout delay based on a timer. Once some ms pass, the RESET will transition to the previous state, so I would probably need a microcontroller in order to handle the logic + a MOSFET, which would add further more current consumption to the system

author: nfmax
author_rank: Super Contributor
timestamp: January 26, 2018, 08:39:39 am
content: I designed a similar circuit for a 12V lead acid battery, which might give you some ideas. It has almost zero current consumption in 'protected' mode:https://www.eevblog.com/forum/projects/battery-undervoltage-lockout/msg1060148/#msg1060148

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: January 26, 2018, 10:35:51 am
content: I've been playing with a custom linux on the kindle, it runs fine down to 3V but any peak @~2.9v and the bms shuts it down for good. Then if you take a meter and read the batt voltage some minutes later it's 3.3 or 3.4V, you say cool, let's turn it on, well, no, it shuts down again in the middle of booting because a 2.9V peak happens again. So the voltage is apparently 3.4 but the batt's internal resistance is so high that it can't cope with any moderate current loads. I think that's the reason why coulomb meters/batt gauges like that bq (the kindle has a bq too) you mention exist: you can't know, not reliably, the batt SoC by looking at its voltage alone.

author: alinp
author_rank: Newbie
timestamp: January 26, 2018, 01:01:13 pm
content: I've also though about a coulomb meter/battery gauge, but that's not the case with my application as I want the user to connect a Li-Ion battery with any capacity he wants. So I can't use such a meter as I do not have a battery with a known, fixed capacity that's to be used with my system.I've took a look at @nfmax circuit, but that's above my knowledge for now. If I would see a simulation run with that kind of circuit, I might be able to understand far better how it works and maybe adapt it for a 3.6V Li-Ion battery.As for now, I was looking atTPS3806. I still waiting for MultiSIM BLUE to install, simulate a circuit with TPS3806 and see if it works. I'll let you know if it does.Later edit:Hysteresis may not be enough for this kind of a circuit. I was also thinking about latching. One solution might be the one posted by @lowimpedance onthistopic (see the last post), but that would also need to be tested/simulated before I can put my trust in it.

author: alinp
author_rank: Newbie
timestamp: January 26, 2018, 02:46:01 pm
content: So I've managed to simulate the circuit with TPS3806, but unfortunately the outputs stay at 0V no matter what. (see attatched printscreen from MultiSim). Am I missing something?R1 = 270k; R2 = 500k; R3 = 16.5kTaking a look at TPS3806datahseet; it should give me the values that I'm looking for:V(LSENSE) ~ 3.3VV(HSENSE) ~ 3.5VI was planning on adding some MOSFETS and that would have done the job, I think. Unfortunately the simulated circuit doesn't seem to work. Any idea on that?

author: alinp
author_rank: Newbie
timestamp: January 29, 2018, 05:00:33 pm
content: After experimenting with more ICs like MAX8212 (https://goo.gl/BmcTeM) or TPS3806 (https://goo.gl/hh56ea), I think that I've found a better solution by using:- 1 micro/nanopower op-amp- 1 voltage supervisor- some MOSFETsThe solution is based on:- LTC1540 as the one op-amp- BD5233 as the voltage supervisorIt's a simple, yet elegant design, based on the schematic in Fig.3 which can be found overhere. You can check the schematic my clicking on the simulation link down bellow.Link to the simulation, clickhere.Simulation raw code:Code:$ 1 0.000005 0.6798259793203881 76 5 43w -80 96 -32 96 0172 -80 96 -80 144 0 6 3.234 4.3 3 0 0.5 Voltagef 320 128 320 96 9 1 0.2w 288 96 304 96 0w 336 96 448 96 0w 448 96 592 96 3r 592 96 592 160 0 10g 592 160 592 208 0w 320 256 320 320 0f 352 352 320 352 0 1.5 0.2w 320 336 320 320 0g 320 368 320 464 0w 352 352 448 352 0r 448 352 448 224 0 10000w 224 96 224 144 3w 320 256 320 128 3w 448 224 448 96 3r 224 144 224 240 0 1000000w 224 240 224 256 0w 224 256 320 256 3w 144 96 224 96 0w 224 96 288 96 0s 672 480 672 544 0 1 truew 672 464 496 464 0g 448 480 448 592 0w 448 448 448 352 0w 480 464 496 464 0f 176 352 224 352 0 1.5 0.02w 224 336 224 256 0g 224 368 224 464 0w 112 352 176 352 0r -32 240 -32 336 0 1000000r -32 336 -32 432 0 510000g -32 432 -32 464 0w -32 96 144 96 3w -32 224 -32 96 3w -32 224 -32 240 0w 16 336 -32 336 0w 16 368 16 416 0R 16 416 16 464 0 0 40 1.182 0 0 0.5a 32 352 112 352 1 3 0 1000000 1.182 1.092278145695364w 16 336 32 336 0w 16 368 32 368 0x 562 437 843 440 4 20 Open\sDrain\sVoltage\sSupervisor\sf 480 464 448 464 1 1 0.2w 672 480 672 464 0g 672 560 672 592 0w 672 560 672 544 0r 496 464 496 352 0 10000w 496 352 448 352 0x 555 450 854 453 4 10 Normally\sOpen;\sClosed\sby\sVoltage\sSupervisor\swhen\sV-CELL\s<\q3V3x 625 136 679 139 4 20 LOADx 252 81 410 84 4 20 Main\sSwitch\sMOSb 0 304 146 478 0x 3 284 152 287 4 10 LTC1540\sNanopower\sComparatorx 11 296 140 299 4 10 with\sbuilt-in\s1.182V\sreferenceb 720 457 624 610 0x 726 535 848 538 4 10 BD5233\sVoltage\sSupervisorx 400 468 432 471 4 10 P\sMOSx 236 351 268 354 4 10 N\sMOSx 276 351 308 354 4 10 N\sMOSx 337 140 369 143 4 10 P\sMOS