Li-ion charger IC accepting >15V input and low quiescent current - Page 1
Forum section: electronics / projects

author: okw
author_rank: Frequent Contributor
timestamp: March 14, 2023, 10:17:15 am
content: Does anyone know about cheap and reliable single cell li-ion charger ICs that accepts at least 15V directly (I'm using it in a car), and has a very low quiescent current?Currently I'm using TP4056, but it's drawing a bit quiescent current (760uA, maybe I have a fake one, datasheet says typ 55uA), and more importantly it can only accept <8V (so I step it down to 5V with a MP2315 - MP2315 has excellent efficiency, but it adds cost, complexity and PCB space).No need for high charge output, the circuit (MCU, GPS, GSM, etc) will draw directly from the charger output (helped by some yet undecided circuitry), I want the battery to stay at 70-80% at all times (just occasionally maintaining charge).I've looked at TP5100 and it accepts 4.5-18V. Found it at LCSC (part number C379389), but that datasheet says 4.5-10V. I'm confused.I've also looked at TP5000 and TP5600. Any others I should consider?There are tons of BQ and MCP, but they can be quite pricy.Also, it's going into production (1000 pcs pr. batch), so I need availability.PS. I've also posted at stackexchange

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2023, 11:29:03 am
content: Even if you do get one that can handle such high voltages, you have to keep in mind that these are like linear regulators, they'll throw out the difference between input voltage and output voltage in the form of heat.So say your input voltage is 13.5v and output is 4.2v and you charge at 0.2A (200mA), your chip will dissipate almost 2 watts.It makes more sense to use a dc-dc converter (with automotive protections) to obtain 4.5v...5v and then use a charger with some pass through functionality or a source switch to switch between output of dc-dc converter and the battery.

author: okw
author_rank: Frequent Contributor
timestamp: March 14, 2023, 02:08:42 pm
content: Isn't the TP5100 a buck?

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2023, 02:54:14 pm
content: tp5100 happens to be a switching regulator, but majority of single cell chargers are linear.Datasheet says absolute maximum is 20v, and it seems the chip is mostly aimed at the 2S battery packs, but it may work with one cell as well. Looking athttps://voltiq.ru/datasheets/TP5100-datashhet.pdf- maybe other companies clone it and make it work with less maximum voltageWhen you do the math, keep in mind that you don't pay just for the tp5100 you also pay for the inductor, diode, potentially some mosfets, and the pcb space ... while you could have a switching regulator in front of a linear charger that could also provide the power for your stuff when input voltage is present.

author: okw
author_rank: Frequent Contributor
timestamp: March 14, 2023, 03:14:31 pm
content: True.I need 3.3V for everything, so another switching regulator is needed. Do you know any fool-proof circuits that picks up the input voltage depending if i have 12v or not? So it picks up 5v from the first switching regulator if 12v is present. And if not, picks the li-ion battery directly.

author: Peabody
author_rank: Super Contributor
timestamp: March 14, 2023, 10:08:45 pm
content: Two diodes would do that for you. The source with the highest voltage would be picked automatically.Or if you don't want a diode voltage drop in the battery line, a mosfet could be used.

author: okw
author_rank: Frequent Contributor
timestamp: March 14, 2023, 10:24:18 pm
content: Thanks. I just found this. How would the slight different placement of the schottky and extra 10R differ?

author: thm_w
author_rank: Super Contributor
timestamp: March 14, 2023, 10:50:22 pm
content: I don't like that schematic, if 5V is present, it will feed through the schottky and FET into the 4.2V lithium right?

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2023, 11:00:08 pm
content: I've suggested this IC in another thread, TPS22933 :https://www.digikey.com/en/products/detail/texas-instruments/TPS22933ARSET/3725886It's a 3 input auto switch with a fixed 3.6v 50mA max regulator built in.Possible downside would be the maximum voltage of 12v (absolute maximum 14v)Maybe you can use it some way ... for example have some IC powered by the ldo monitor the input voltage and if the car battery goes down below 11v or something like that, disable the dc-dc converter that converts car battery voltage down to 5v and then the IC would switch to the lithium battery output and continue.

author: Peabody
author_rank: Super Contributor
timestamp: March 15, 2023, 01:58:24 am
content: Quote from: thm_w on March 14, 2023, 10:50:22 pmIndeed. If you draw in the mosfet's body diode, that will become apparent. You don't want the battery to be charged that way, not a lithium battery at least.In addition, it's hard to see what R1 is doing there. It looks like the mosfet will be on even when 5V is present. Just have R2, at 10K.

author: okw
author_rank: Frequent Contributor
timestamp: March 15, 2023, 03:15:08 pm
content: Thanks. After looking around, I would like to substitute the 12V->5V step down + TP4056 battery charger (linear), with just a TP5100 (buck). I have to experiment to see what is most efficient (quiescent + charging) and has acceptable low noise, etc.We plan to have a current/voltage monitor (ina3221) on 3 rails (12V, charge through the battery, and direct draw from the TP5100).During storage (could be 3-5 months) the MCU will wake up every x days and maintain charge at 70-80% (it's better than 100% for storage right?).How do we realize the mosfet picker when we only have one source for both charging and "direct draw"?

author: Peabody
author_rank: Super Contributor
timestamp: March 15, 2023, 04:55:32 pm
content: The two diode selector model will give you 12V through one diode if the 12V supply is connected, or as low as 3.6V or so from the battery if the 12V supply is not connected. So you will need another buck converter to produce the final 3.3V supply from either source. I don't know what's available to handle that range.Anyway, the circuit is the same. Below is one for the TP4056, but it should work the same with the any charger.But this circuit would keep the battery 100% charged. In fact, it would charge the battery, if needed, even when your device is switched off.Edit: This reply originally showed a 12V supply with the TP4056, which of course won't work. I've changed the picture to show the TP5100.

author: okw
author_rank: Frequent Contributor
timestamp: March 16, 2023, 06:50:25 am
content: We used a linear LDO (ap7366, Vin>6V) for final 3.3V as it has much less noise, complexity and cost than a buck. And since we tapped into the 4.2V rail, it generated negligible heat.We will software control the charge enable, so it will only maintenance charge when the vehicle is running (12V will be 13.5-14 when the alternator is charging) or when we detect the li-ion is getting below some lower threshold.Would it be a bad idea to still tap into the TP5100, but disconnect the li-ion with a mosfet (and have the mosfet turn on in the absence of 12V or when MCU is initiating charge enable)?

author: Peabody
author_rank: Super Contributor
timestamp: March 16, 2023, 02:23:32 pm
content: I don't understand what you're asking. Could you post a drawing?

author: okw
author_rank: Frequent Contributor
timestamp: March 17, 2023, 02:47:32 pm
content: Don't kill me. I'm not sure how to draw it. But my idea is to have the charger active at all times and directly supply 4.2V into VIN of the 3.3V regulator, and keep the battery disconnected with a MOSFET. Then occasionally connect the battery (signal from MCU) when a charge is needed, or automatically when 12V is lost.Since TP5100 is buck, having a linear 3.3V regulator would greatly reduce noise (and not add to space, cost and complexity by having a 12V->5V buck before the 3.3V LDO regulator).Perhaps it's a stupid idea (since I loose the features of a charge management chip, timeout, temperature cutoff, etc)?

author: Peabody
author_rank: Super Contributor
timestamp: March 17, 2023, 03:25:11 pm
content: I don't know if the TP5100 will output anything if there's no battery connected, or what voltage it would produce. And would it terminate charging at some point? Well I can't say this won't work, but I've never seen anything like it. I think you would have to experiment with a TP5100 module to see if this works.

author: okw
author_rank: Frequent Contributor
timestamp: March 17, 2023, 03:35:40 pm
content: Good point about outputting anything without a battery connected. I'll order a few and experiment with it.But from a professional standpoint, is it a bad idea? To base your whole power supply design on this "experimental" approach.

author: Peabody
author_rank: Super Contributor
timestamp: March 17, 2023, 04:31:01 pm
content: I'm not a professional, so I can't answer that. I just don't know if it will work at all. Lithium chargers are built to start with constant current, then go to constant voltage, then terminate. I just don't know what the TP5100 will do if there's no battery connected. I suspect it will shut down, but that may depend on the load current.