Problem Report
We have a system that uses a BQ25672 as a battery charger for a LiPoly 4S battery pack. Although the charger works on the BQ25672EVM, we are having problems with our design. Although the schematic is the same, the capacitors are physically smaller, and the layout is not the same as the EVM. (But, different enough to keep the IC from working?)
See attached pdf for more details.
HI Ed,
Unfortunately, this device is very sensitive to layout especially the PMID and SYS capacitors. The input current and battery charge current sensing circuitry do not read correctly unless the 100nF PMID and SYS capacitors are placed as close as possible between the PMID and SYS pins and GND without vias. That means that the SWx lines to the inductor must be routed under the IC and then through vias to either the bottom of the board and back up further away from the IC with C1 and C2 being the 100nF. This adds negligible resistance and inductance to the inductor's large inductance and DCR. The datasheet recommended layout is shown below.
Also, with a 4S battery pack that can be hotplugged, we recommend adding a TVS to protect the 20-V rated BAT and BATP pins from ringing at the hotplug.
Regards,
Jeff
