Other Parts Discussed in Thread: BQSTUDIO
Dear Sirs,
At the moment we are developing a battery charger using a the BQ40z60. We have manufactured and assembled 10 PCBs.
The design of the PCBs are based on the bq40z60EVM synchronous buck converter. The inductor remains the same as the EVM (2,2uH 5A) , a shunt series od 0.01 Ohms and output capacitor of 10uF35V.
Feedback needwork is the same as EVM (332K and 26K1). As our battery charger will be powered from a 24V Power supply, we decided to change both power mosfets to the BUK98150-55A/CUF. R gate of both mosfets are 0 Ohms. Further information (Sch / layour may be shared with you prioir NDA)
We don’t need any temperature measurement from battery, so no thermistors are used. The battery are 4S LiPoly batteries 2.4Ah or 1.7Ah. These batteries have only two wires (+ and -), so we do not have access to battery cells.
We use BQStudio using the EV2300 to set up the BQ40z60, calibrate the device and to test it. In fact, some of the PCBV begins the battery charge, althought they do not finish the charge completely, even the system gets calibrated and configured. At this point we have the following questions:
1) Can the bq40z60 work with a 4S battery with no cells access? We found that the chipos was unable to read battery voltage properly, so, we added a 4 series resistors of 1MegOhm to “simulate” the voltage of every cell. This seems to work, but cell voltage on BQStudio appears quite unbalanced (some othe them 4V, other 2.9 V, ….)
2) Do we need to calibrate every PCB during the production? Since all PCBs are the same, we think that have one PCB calibrated, we could use the same calibration file for the rest PCB. Is it correct?
3) We have detected different behaviours between bq40z60. Some of the charge the battery. To do so, we calibrate current and voltage, then apply a reset and then, click on CHARGE_EN. Some of bq40z60 keeps reading OK the battery voltage, but some of them report a seriurs battery voltage drop. We are using a 4S lipoly battery. They measure 15V when not charging, and suddenly, 10V when charging. However, the measured volttage en BAT pin with a tester remains 15V... Any idea of this?
4) Of course all the bq40z60 have been set up before charing (DA configuration register set 4S battery, no tenmperature measuring,....) As the same of question #2, can we have a single configuration file and apply this configuration to every Bq40z60?
5) If we measure the voltage on the gate of the up-side MOSFET, wehave the attached waveform. This osciliationm during the T_off is quite surprising. Any idea?
We can share the *.gg files with you.
Thank you very much for your support. Keep in touch,
Carlos
