Other Parts Discussed in Thread: BQ24074, BQ51050B, BQ24075
Hi
I used the circuit as shown in attached schematic .
It uses BQ24074 for USB charging
BQ51050B for wireless charging
BQ27421 as Fuel Gauge
We use Li- ION 4.2V / 1200mAh battery
Recently we started seeing problems on USB charging side
First occurrence:
After battery had been disconnected over the weekend.
Connected the battery and the SoC reported 17% and Battery Voltage as 4.128V.
Connected the USB charger, firmware detected and switched to charging screen and for more than 1/2 hour the capacity did not increase - still showing 17%.
Strangely the rolling bar indicator moved slowly to about the 17% mark then jumped to 100%, then went back to moving from 0 to 17% and repeated.
Disconnected battery, reconnected and now the startup screen showed 23% and 3.something volts. (didn't catch the decimal places). Connected the USB charger and now the charge screen is sensible, showing normal rolling bar indicator and charge capacity is slowing increasing.
I think maybe the odd jumping to 100% on the rolling display is perhaps the USB charge done line activating? But then the firmware sees the capacity is low so switches back to charging state.
2nd occurrence:
Got it in a state now:
Voltage swinging between 3.808 and 4.187 (I think depending on state of USB charging - see below)
State of charge 59%
USB_CHG_PGOOD is low (USB connected)
USB_CHG_DONE is oscillating
But it is likely the firmware is also oscillating the EN_USB_CHG because when it sees USB_CHG_DONE it switches to the USB charge finished state and turns off EN_USB_CHG. But then it sees State of Charge too low and switches to USB charge state and turns EN_USB_CHG on again.
I think the driver is the hardware is setting USB_CHG_DONE high for some reason even though the capacity is low.
Now I have finished typing this it has settled down again with these values:
Voltage: 4.186
State of charge: 60%
USB_CHG_PGOOD is low (USB connected)
USB_CHG_DONE is low
Interestingly there have been some issues reported in another instrument by a competitor who are using BQ24075 (another chip in similar series). & they have issues with USB charging & capacity reading as well. All we know is that they have to open the instrument, disconnect the battery, reconnect & it starts working
So, the question is: is the problem we are seeing related to USB charging IC or Fuel Gauge?
I understand that Fuel Gauge IC needs charge & discharge cycle to learn. Is one charge / discharge cycle enough for it to learn? & battery has PCM on it that has IC which disconnects the battery from Main circuit at Low voltage. This means that Fuel Gauge will loose power to it every time PCM's protection IC kicks in so does the Fuel Gauge need new learning next time the battery is connected? In this case this IC is not good for us because in field we want it to show SoC accurately every time we charge or discharge the battery. Also, we charge the battery to 90% SoC only as with wireless charging, it was taking hours when it reached near full capacity to terminate. So, we terminate it earlier. Could that have any impact on Fuel gauge learning?
Do any one of these ICs have any issues reported on the reliability side? We have put them in design which we will be selling tens of thousands per year and last thing we want is product recall.
Other issue that has been reported is 'Fuel Gauge ICs' getting damaged during Assembly process. Apparently they are too sensitive to heat even when assembly house used the recommended temperature profile for soldering of these ICs. This meant that we had to take all ICs off board & solder them using hand soldering (reflow) method. Any such issues reported for Fuel Gauge IC?
I understand that there have been issues with supply of chips as well (due to covid) which means we might have to look for another device as at the moment we would not be able to sell any of these products before mid next year or even after due to IC shortages. So, as we are going for re-spin, it would be good to use a chip which is reliable
Looking forward to hearing from you
(screen dump of schematic is shared here) Happy to share the full schematic if you could send me a message with app engr contact please
