Charging Current Based on MAX1873

[Chimicron]

Hi,

I am designing a kind of charging module which is base onMAX1873REEE+
. Could anyone here give me some suggestions?

My goal is to charge up the polymer battery--8.4V as well as the DC electrical source--12V. However,when in debugging, it’s OK if the current that DC electrical source provides is 1A. In another words, the Charging current is about 1.5A. But if the charging current is about 3A, there are some wrongs occurred here.In the beginning, the DC electrical source shows it’s 2A charging, but it will drop quickly and here just is 0.3A. Does anyone help me?

Thank you in advance.

 

[FAST6191]

Do we have a device this is for (we cover a wide variety of consoles on this site, and indeed anything vaguely considered a game playing machine is probably in play for this sort of thing and if you want 12V it is very likely to be that) or is this just someone's electrical engineering homework?

https://www.digikey.co.uk/en/products/detail/analog-devices-inc-maxim-integrated/MAX1873REEE/1513342 appears to be the chip in question and has a datasheet link there too
https://datasheets.maximintegrated.com/en/ds/MAX1873.pdf

Anyway so you have an 8.4V presumably LiPO cell and want to get 12V out for your circuit (guess some form of boost converter as that is well within range of such things, though 1A presumably continuous output might need a slightly beefier one than some of the smallest presently available).

You sound like you might have an example circuit already which starts at 2A but drops down to 0.3A after a while. That is a fair drop but still within some kind of range of standard lithium charging.
Alternatively 8.4V is not a standard voltage for any kind of common cell so you presumably have a few in series there (maybe some more in parallel) which your chip there looks like it is built to handle. If one or more of those has failed (could be bad out of the box, you could have cooked it if you messed something up) then you might take in charge quickly initially but it soon saturates and will drop back down which also will give you minimal battery life (see the common thing of only one cell in a tool battery/laptop battery failing and dragging everything else down with it after minimal lifetime -- lose a whole cell with 2.7V say and if the cutoff is 9.2 compared to the resting 12V and even if all the others are basically 100% you are going to be limited).

3A looks like normal range for the chip as well, though it has provisions to set it lower if for some reason you want to do that (maximum lifetime, limited heat dissipation in the battery*, limited source current capacity... various other reasons).

6 ICHG/EN
Battery Charging Current Adjust/Shutdown Input. This pin can be connected to a resistive-divider
between REF and GND to adjust the charge current sense threshold between CSB and BATT. When
ICHG/EN is connected to REF, the CSB-BATT threshold is 200mV. Pull ICHG/EN low (below 500mV) to
disable charging and reduce the supply current to 5μA.

*though it reckons in some of the graphs above that 3A charging should be pretty efficient compared to higher currents so who knows.