Dear Sir,
I have designed an hand-held RFID reader using BQ25120 as a central power management unit (battery charge, system power rails). The device has some buttons that let user make actions on device. One of this buttons is also connected to the PMIC MR line, in order to let the device exit ship mode on button pression and also to let the user to RESET the PMIC in case of emergency. We have integrated with success the BQ25120 in our electronic board and all requirements have ben satisfied (battery management, line regulations, LDO, ship mode etc etc).
So we have produced and sold some hundreds of units and now, after some weeks of usage, we are receiving back some units bricked, with BATT voltage on PMID and SW off. All units we receive back are in this situation:
VBAT is nearly 4V
PMID is nearly 4V (this is not expected)
SW if off, 0V on it
LDO is off
MR line is stable at 600mV (this is interesting!!)
Trying to recover the device pressing the mechanical switch connected to MR does not make any change, also keeping pressed for more than 10 seconds (our PMIC programmed reset time). MR line is directly connected to a PCB mounted pushbutton and to uController port in order to let pushbutton status readable. As we know, pull-up is internal on MR line so no external pull-up are present. The only thing I've added to the design respect to the TI reference design is a little capacity (100nF) between the MR line and GND in order debounce the button contact line. The capacity is very close to the button.
The only way I have to let the device restart, and the PMIC work properly, is to unplug battery cable and then replug it. Last but not least, I have found that if I remove the 100nF capacity from the MR line when the device Is bricked (hence without unplugging battery), after capacity removal pressing MR button let the device restart properly. This is the reason why I think the capacity has an effect on PMIC behaviour.
Here you can find attached the schematic sheets out PMIC integration, to which I've added the MR pushbutton connection. I can provide other sheet if necessary, but in private, by the way, I see no reason to do so. Please let me know if you have some hints for me.
P.S.
We have another lot of board in production, this time we are assembling with newer BQ25120A part.
Thank in advance for your attention.
Bye
