Hello, I am making a battery charger for a 6S 2900mAh lipo battery pack charging at 2.9A and was wondering if you could have a look at my schematic and see if there's anything wrong? I am using BQ24650 for the charging and the BQ76942PFBT for cell balancing/monitoring/protection. Thank you!
Hello Steven,
have I incorrectly set it to 12.6 and not 22.2?
Yes, I recommend refering to section 9.3.1 Battery Voltage Regulation of the datasheet. You can also find this equation in the schematic checklist.
I reccommend refering to the BQ24610 schematic checklist: BQ24610_BQ24650_Schematic_Checklist.pdf.
I will let the Battery Monitoring team comment on the schematic design of the BQ76942PFBT.
Best Regards,
Christian
Dear Steven,
Overall, the schematic looks pretty good, but I do have few adjustments that should be made:
1. A NC_2 is tied to a cell's voltage. I would change it to floating
2. Capacitance's for the cell input filters (C34, 35, 33 etc) should be 0.1uF rather than .22uF.
3. While not required, it is recommended to have 0.1uF capacitors going from SRP to VSS and SRN to VSS
4. Capacitor C8 (and C40) on REG1 is not tied to VSS
5. This also isn't required, but it helps the accuracy of thermistor measurements to place a capacitor in parralel with RT2 and RT3 (Roughly 470pF)
6. Not sure if this is connected or not by looking at the schematic, but I wouldn't tie Fuse to BREG if it is actually connected
I hope this helps!
Best,
Asher Nederveld
Hi Asher, thanks for the feedback! Could you please confirm that the following is correct? On the reference the net is 7P but mine is pack+
Kind regards
Steve
Hi Steve,
Your layout will likely work but the mixed ground may cause switching noise to affect the accuracy of the charge current measurement across R21. You don't necessarily have to have separate switching/power and signal/analog grounds (connected only at the IC itself) if you place/route all of the power components (Q1, C19, C20, C24, C25, C4) in a tight loop. But on your board, the sense resistor R21's filter cap will see switching noise from output capacitors C24 and C25 and REGN capacitor C4 as shown below:
Also, input capacitors C19 and C20 are okay if more vias are added to the ground side but they we be even better if flipped 180 so the ground didn't have the via to get the ground of Q1. That would mean that the other signals would have be via'd which is okay. Also, having short LO/HIDRV gate drive traces back to REGN cap C4 is also preferred but, I admit, is difficult on this part due to its pinout.
Lastly, the large PH node copper power with ground immediately underneath contributes to EMI.
Regards,
Jeff
HI Steve,
VFB should be 100/(500+100) of the battery voltage, close to 2.1V if battery is fully charged. Almost 8 V is too high.
And with input power > battery voltage attached, VCC should be at least a diode drop below the applied adapter output voltage due to the PFET body diode:
can you confirm component installation?
Regards,
Jeff
HI Steven,
If VFB pin is below 2.1V, then the battery is not fully charged. The BQ4610 is a buck charger so the input voltage must be greater than the battery voltage by at least 150mV for PG LED to be on. If both STATs are off then one of the following faults is occurring:
What is the battery voltage at this time? Has the timer expired?
Regards,
Jeff
Hi Jeff,
I think this is the last question (hopefully!) I think everything is working now, however I have set the charging current to 2.9A and it seems to be charging at 1.7A, have I worked out the resistor values wrong?
Kind regards
Steve
Hi Jeff,
Unfortunately I cant test any of them because they caught on fire and look like this:
This particular board didn't have the IC soldered on at the time and it still went bang. I will add a series resistor on the next iteration, is this likely to solve the issue? The board works great when its not on fire!
Kind regards
Steve
