TPS61322: Paralleling two regulators w/ 2 coin cells to get more current

Hi, Minqiu.

Thank you for reply.

The coin cell is CR2032 (3V), and its voltage range is 2.6V ~ 3.2V. If low battery status is detected, to change cell will result in data loss (ex: real time clock). Since we have 2 cells, we can replace old cells respectively to new cells.

The device equipped 2 cells can run for at least one half year. I am not sure what will happen if one cell charge another. But anyway, it sounds not a good news.


Best regards,

Louis

Hi Louis:
I haven’t heard back from you, I’m assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

Hi, Minqiu.


Last Friday, according to your opinion, we decided to parallel two cells. Only one TPS61322 can reduce cost and avoid some issues (current-sharing or others). Thank you very much.



Best regards,

Louis

Hi, Minqiu.

I have another idea.
Is it possible to combine 2 cells with TPS22976N (reverse current protection) and TPS61322 to avoid current-sharing ?


Best regards,

Louis

Hi Louis:
The current-sharing is not necessarily fatal. Current-sharing issue means the current from two cells maybe not same. It's caused by the difference of cells, converters IC and other device, even in same part number. If one of the cell (A) share heavier load than another cell (B). The life of cell A will shorter than B, and shorter than typical lifetime. I will do bench test to figure out the influences. But please understand I have a lot work, and the test may finish after one week or more. And the power supply I used couldn't behave as same as the cell. So you may need to do the test too.

TPS22976 is my other colleague's part. I have read the datasheet, and it seems have no reverse protect function: there is a diode between Vout and Vin.LM74610-Q1 may be the proper product. But unfortunately, it could protect the cell be charged but do nothing for current-sharing in my view.

By the way, is two cell parallel an normal usage for your customer? It's my first time to meet this need. It's very interesting and worth thinking. So thanks for you.

Hi, Minqiu.

I read TPS22976 datasheet again and found that the reverse current protection only acts when the device is disabled. If two cells are used simultaneously, cell w/ lower voltage may be charged by cell w/ higher voltage.

In this project, I'm informed that to parallel cells is forbidden. I inquired about two cell paralleled. Our customer replied that it was an normal usage before, but it seemed something goes wrong. They don't tell me what on earth happened.

Next week I will do some test you mentioned. It's very helpful. Thank you very much.

By the way, I only find bulk regulator with reverse current protection on TI website. Can you advise on any boost converter with reverse current protection?


Best regards,

Louis

Hi Louis:
We have lots of products with reverse current protection, such as TPS61099: www.ti.com/.../description

What's your value most? In my view, there are three solutions:
1# Two cells parallel. It's normal and easy solution, but it has the risk that one may charge to another.
2# Two convert parallel working together, like TPS61099.
3# Two convert parallel and single circuit work at one time, another is just for back up.
4# Base on 2#, using TPS21xx power mux to select the power rail.

Please confirm how much current the cell could be charged? May some nA OK? Or absolute none?

Hi, Minqiu.

Thank you for the solutions.

According to all documents from our cell suppliers, the cell shouldn't be charged.

Before getting reply from you, I've noticed TI power muxes product. But I have another mission: to reduce cost due to budget. I measured power consumption several time. The whole system current is about 20mA. Thus, the solution 3 is the best one. I will survey TI converter solution to accomplish this project. Thank you for your help again.


Best Regards,

Louis