Information about bq51050B

Federica,

1) I would suggest starting with the same value as in the bq51050EVM.  That is R17 on the EVM and has a value of  42.2k as you suggest.  For your implementation, a value close will work.

2) Since you chose the Vishay coil as used in the EVM, I would suggest starting with the same values as in the EVM as well (68nF, 68nF and 47nF).  I would strongly suggest using 3 capacitors in parallel to achieve 183nF.  The full current goes through these capacitors so choosing capacitors with low ESR and good thermal characteristics is critical.  Use an X7R type if possible.  Physically larger is better for the ESR and thermal (in general).  The EVM uses 0603.  This works well.  0804 are sometimes easier to work with during hand solder.  Finally, make sure the voltage rating is 50V.  Using lower voltage ratings will reduce the effectiveness of the system.  The EVM uses 1.8nF + 0.1nF for the C2.  Your choice of 1.6nF would be fine for your application.

3)  Once again referring to the EVM, I would suggest using two 10uF capacitors on RECT with a 0.1uF for high frequency spikes.  The BAT pin value of 100uF would certainly be enough.  You could reduce that.  Generally, I like to have more capacitance at the RECT than the BAT.  More capacitance at the BAT means the RECT has to charge that before anything else can happen.  A large transient on the BAT must be replenished.  If the RECT capacitance is greater than the BAT, the system will respond more favorably.

If you have further question, I will try to assist.

Regards,

Dick

Federica,

Correct, R6 and R12 are not required.  

If you are interested in the details, they are covered in the "Communication Modulator" section.  There are two ways to enable communication from the RX back to the TX.  

First  (as is most common and used on the EVM) is using capacitors between AC1/COMM1 and AC2/COMM2 (C8 and C13 on the EVM).  This is Capacitive Load Modulation.  When the RX communicates, it enables the internal COMM_DRIVE FETs and creates a signal on the coil.  The signal is demodulated by the TX.

Second (R6 and R12 on the EVM) is Resistive Load Modulation.  Pulling on the RECT pin will also have an impact on the magnetic field.  The modulation is received by the TX.

I have not seen a system that uses the second method, although it is allowable per the Qi standard.

Regards,

Dick

Federica,

If you want to disable the temperature control function, tie TS-CTRL to ground with at 10k resistor.

If you want to allow the bq51050B to terminate charge if the temperature is too hot or too cold, then you need a thermister tied to the TS-CTRL pin.  See the section on Battery-Charger Safety and JEITA Guidelines.  Depending on the thermister, a simple thermister to ground can work (10k ohms at 25C).  In other cases, as is shown in Figure 25, R1 or R3 or both may be needed.  It depends on the temperature control required.  Selecting R1 and R3 can be difficult.  It can be an iterative process.  See the TS / CTRL section of the Electrical Characteristics table on Page 5.  VTS is typically 2.2V.

Regards,

Dick