Solution Selection

Roberto Imai

Other Parts Discussed in Thread: BQ25100, BQ51003, TIDA-00318, BQ51050B, TIDA-00762, BQ51013B

Hi,

I'm looking for a wireless charger for an upcoming product we are designing.

I'm going to be using a 150mAh battery that can be charged at 0.2C, so just 30mA charge maximum.

I'm looking for help to select suitable ICs to evaluate, preferably ones that TI has evaluation kits that I could use to test without having to spend time designing pcbs just to see how well they would fit the bill for us.

I'd also prefer ones that have or could be used with small coil size. Somewhere in the range of 20mm.

Thanks,

over 9 years ago

0 Dick Stacey over 9 years ago

TI__Genius 14890 points

Roberto,

For charging at 30mA, I would suggest using a combination of the bq51003 wireless receiver, and the bq25100 low power linear charger.

Both devices have an EVM. Additionally, look at TIDA-00318 which is a board made with the two devices in a small 5mm x 15mm solution. The coil used in the TIDA-00318 is 22mm.

Regards,

Dick

0 Roberto Imai over 9 years ago in reply to Dick Stacey

Intellectual 685 points

What is the advantage of using combo bq51003/bq25100 vs single chip bq51050b?

0 Dick Stacey over 9 years ago in reply to Roberto Imai

TI__Genius 14890 points

Roberto,

The bq25100 is a linear charger that is optimized for high accuracy at low charge and termination currents. It can accurately terminate at currents down to 1mA.

The bq51050B is optimized for higher power solutions (up to 5W). As a result, it's accuracy at 30mA not as tightly controlled as the bq25100. The bq51050B will work, but I do not expect you will be pleased with the accuracy of a large distribution of units.

Regards,

Dick

0 Roberto Imai over 9 years ago in reply to Dick Stacey

Intellectual 685 points

Ok, so going with the combo then.
I was looking at TIDA-00318 reference design and the datasheet and got confused on selecting RFOD and R1.
According to the calculations, the max current of the reference design is 250mA, but the description says 135mA.
If in my application the max current is 30mA, how would I go about selecting RFOD and R1?

0 Dick Stacey over 9 years ago in reply to Roberto Imai

TI__Genius 14890 points

Roberto,

The bq25100 is capable of charge currents up to 250mA. The particular implementation in the EVM sets the charge current to 135mA by selection of R7.

The bq51003 sets its maximum current to 300mA by selection of R1 + R2 (generally referred to as RILIM). If you need 30mA charge current, you should choose R7 based on equation 1 of the bq25100 datasheet (RISET = KISET/IOUT). WIth KISET = 135 and IOUT = 30mA, RISET = 4.5k ohms.

R1 and R2 should be chosen to set the maximum output current close to the bq25100 IOUT. 50mA would be reasonable. Equation 2 in the bq51003 datasheet shows RILIM as 6280 ohms.

RFOD (R2) should remain as is and alter R1 for the correct RILIM.

Regards,

Dick

0 Roberto Imai over 9 years ago in reply to Dick Stacey

Intellectual 685 points

Thanks for your help.

I found the design reference for the 19mm coil, which seems a good size for my project.

www.ti.com/.../tida-00881

What about the transmitter side?

Which solution would you recommend so I could use a coil with the same dimensions? 19mm in diameter?

0 Dick Stacey over 9 years ago in reply to Roberto Imai

TI__Genius 14890 points

Robert,

You have a few good options of small TX coil TIDA designs.

Check the TIDA-00334.

Check the TIDA-00415.

Check the TIDA-00762.

Regards,

Dick

0 Roberto Imai over 9 years ago in reply to Dick Stacey

Intellectual 685 points

Does BQ51013B work the same as the BQ51003 for my purposes, since my load is very low?
I'm trying to find a different package than DSBGA.

0 Roberto Imai over 9 years ago in reply to Roberto Imai

Intellectual 685 points

Ok, So I decided to try out the BQ51013B, but I'm having a small issue.

Either the receiver stops receiving or transmitter stops transmitting for about a second or two every so often.

I'm using coil WE 760308101105 in the transmitter and coil WE 760308101214 in the receiver.

Attached are my transmitter and receiver schematics.

Any suggestion?

1460.Receiver.pdf

2100.Transmitter.pdf

0 Roberto Imai over 9 years ago in reply to Roberto Imai

Intellectual 685 points

Any comments from anyone?

0 Dick Stacey over 9 years ago in reply to Roberto Imai

TI__Genius 14890 points

Roberto,

My apologies for the long delay. I missed this reply.

The TX coil you note is 3.3uH with the standard TX coil being 6uH. Did you re-calibrate the TX resonant frequency?

What load are you using for your testing? Does the response vary with load?

Dick

0 Dick Stacey over 9 years ago in reply to Roberto Imai

TI__Genius 14890 points

Roberto,

My apologies, I completely missed this post.

Did you set the resonant capacitors (AC1) to account for the higher coil inductance in the RX coil? These would be C1, C2 and C3 on your RX schematic. Same question for the TX (C17, C18, C19).

What is the distance between the coils?

Regards,

Dick

0 Roberto Imai over 9 years ago in reply to Dick Stacey

Intellectual 685 points

I'm using to charge a 170mAh battery. That's the only load.
I noticed that the problem is with the TX side as it works fine with another transmitter from another manufacturer.
The RX side works fine with the other transmitter.
I have not changed the capacitors.

0 Dick Stacey over 9 years ago in reply to Roberto Imai

TI__Genius 14890 points

Roberto,

Thank you, this is good information. If you are using the smaller TX coil with the 3.3uH inductance, then your capacitance should match that as in TIDA-00415 (0.22uF + 0.22uF +0.22uF).

Regards,

Dick

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