Other Parts Discussed in Thread: TIDA-00669, TIDA-00668, BQ51003, TIDA-00318
Hello I am developing a product that I am planning to use the bq51050B for Qi/WPC wireless charging. I am wanting to use this specific IC due to the fact it is a 'stand-alone' charger and does not require I2C and secondly because is Vout is suitable for directly charging a Lithium Polymer. I have developed a schematic already and attached this for your review. I have some questions listed in the schematic that are also listed below for your convenience. I need to be sure the bq51050B will indeed work suitably with a smaller 250-300mAh LiPo as this product has significant size restrictions which limit my battery size.
System Description: 250-300mAh LiPo to be directly charged by bq51050B. There is a simple Reverse Battery protection circuit that is just a simple N-FET that with proper polarity connects BAT- to GND(GND is used by rest of the system). Being that the battery is rather low capacity and this product has the potential to go without charging for some time I want to ensure I can minimize the Quiescent current of the bq51050B which is indicated to be ~12uA by disconnecting the bq51050B from the battery. I have proposed a battery disconnect in the schematic attached seems like this should work but can you please review? Secondarily there are questions about what the Minimum Ibulk(charg current) and Iterm(termination charge) currents truly are. Questions are posed below...
1) Using a ~250-300mAh battery am I correct in thinking I can set a Ibulk(charge current) to ~220mA as a starting point? Secondly being such a small battery capacity I want to be able to have a low charge termination current of ~4mA. I am not clear if this is truly feasible or not?
* bq5105x DS seems to indicate in the specs the Minimum Ibulk that can be programmed is 500mA?
If this is correct the bq51050B simply won't work as I only have room for ~250-300mAh LiPo.
* Iterm ~4-5mA? bq51050B datasheet seems to indicate smallest Termination charge current settable is ~100mA? Is this correct?
2) If the Icharge and Iterm currents can be set to my needs I must find a way to disconnect the bq51050B from the Battery to remove the constant ~12uA discharge as this product could sit for a long time without being re-charged and this constant drain is substantial for a low capacity battery.
* Can I used a simple N-FET disconnect/connect the BAT- to the bq51050B as shown with Q3 and use the RECT voltage to drive the GATE
of the N-FET? Seems like this should work fine but I may be missing something? Would it be better to do a High Side Switch?
Is there a better recommendation to remove the 12uA Iq and disconnect the bq51050B from the battery?
3) I am using a simple N-FET Reverse battery protection circuit that connects BAT- to GND(used by the rest of the system). I am assuming that wherever GND is shown in example schematics in my case this needs to be BAT- to avoid any contentions and be on the Battery side of the Reverse Protection circuit, correct? I.E. - You can see in my schematic I have a debug solder-bridge(SB2) to connect all PGND's to BAT- to effectively bypass the Q3 N-FET.
Thanks in Advance for your help!!
