qi certification for a wearable

If you intend to put the Qi logo, then you must go for certification. If you simply are using the bq51050B, no certification is required.

You would need to contact the Wireless Power Consortium to determine the cost of certification.

Regards,

Dick

Hi Dick,

Thanks for your reply. based on your input we have decided to use Bq51050B .we had prepared a prototype. and we have problems in using it. before explaining about the problems, let me get you some design values we have used.

inductor coil :- WR301025-19M8-G https://product.tdk.com/info/en/catalog/datasheets/wr_rx-coil-wr301025-19m8-g_en.pdf

C1 = 200nf (100nf+100nf),50v

C2 = 2nf(1nf+1nf),50v

R1 = 1.8K ohm

Rfod = 170ohms

Ros = 100kohms

Cboot=10nf, Clamp->0.5uf(2 1uf caps in series as exact 0.47uf not available at this time), Ccomm = 20nf(2-10nf caps in parallel) all 50V caps

Rterm = 2.2Kohms

we have following problems

1.Charging LED blinks some times, fastly some times slowly. Is this expected behavior or not? even in the Qi complaint charger, RED, purple light changes in almost same rate with LED blink some times, some times LED on CHD does not blink , some times, the LEDS at Qi TX stays on purple, but nothing happens on RX side. 

2.Does the above mentioned blink indicate connecting & disconnecting continuously?

3. when Battery is almost drained, I was unable to even get the above behavior. Our device is an wearable with out external charging option, and we are planning to use only WPC ..now we afraid that when battery is almost dead, can the WPC BQ51050B able to charge the battery?

we need your help asap, Thank u

Hi Dick, and one more point to above post, during testing, when a place any metal obj(say a pocket knife) on top of the coil,at that time the LED stops blinking on CHD and stays ON continuously.even on TX side also LED stays purple. however,heat increases.. I doubt if any low current issue? battery I had connected is an 3.7V,200mah battery.. hope the inputs provide enough information needed to give me an better solution, Thank u

Chandra,

From previous post

1, 2:  Charging LED:  The bq51050B CHG pin pulls low when charging is active.  If it is not solid, then the system must not be stable.  Please give me a few more details about which LED you are discussing so I can clearly determine RX and TX responses.  Depending on the TX and its configuration, some TX LEDs may be on, off or blinking depending on the state of the power transfer.  A good indication of the power transfer can been seen on the RECT pin.  This is the pin that shows the rectified voltage created from the AC1/AC2 signals.  Watch RECT at initial power and during the system activity.

3:  The bq51050B responds to the voltage on the battery.  If the voltage is below VLOWV, then it will be in Pre-charge mode with a reduced current which is about 20% of fast charge.  If the battery is below VBAT(SC) the system interprets this as a short and limits the current to IBAT(SC) which is about 18mA.

Metal Object from this post:  The bq51050B sends its power consumed information to the TX.  The TX does its own calculation of what it is sending to the RX, then compares it to the RX reported power.  Based on the delta between the two values, the TX should continue to transmit power or disable power. It is not the decision of the RX.  What transmitter are you using?

Regards,

Dick

Hi Dick,

Thank you for you kind reply. I am talking about the LED connected to CHG pin. as I can understand that now the system is not stable.

in my understanding, system is connecting and disconnecting continuously.

on RECT pin--  voltage rises to around 3.5 to 4 volt and with some pulses it keeps in that range for approx. 1sec and then backs to zero and after 300 to 400ms the cycle starts again. ...

I am using an qi compliance transmitter which is similar to the one in the link http://www.ebay.in/itm/262394714733?aff_source=Sok-Goog  

I had removed the cover of TX, and placed the coil directly on the other coil, at that time ,even there is no battery ,the previously mentioned, CHG pin blink,RECT voltage pulsing takes places continuously. but when I put on top coil with enclosure, I don't see any thing happening with out battery.

1.for the coil I had mentioned in previous post, does the calculation correct?

2. what should be the key components I should look in to , to make the system stable?

3.is there any way ,I can check if the coils has matched the proper capacitance, to check if coil and caps are matched for resonance?

I may need your help. I will be checking and fixing these circuit ,almost in live based on your responses. awaiting for your reply. thank u

Chandra,

RECT needs to approach 7.5V to 8.0V.  If it is not reaching that high, the coupling is not good enough.  The bq51050B never communicates back to the TX that it is a legitimate RX so the TX restarts.  Based on the coil you used, the Cs and Cd are good.  I believe the shape of the coil may be reducing the coupling.  If possible, use a coil in similar shape to the charger - as a debugging step only.  If you have a coil from a bq51050BEVM I suggest starting there since it is a know good solution.  Your Cs of 200nF will work (efficiency may be a bit low), but it will tell of if it is a coil / coupling issue.

You also should use a battery or other system to emulate a battery.  If the bq51050B does not sense a battery, it will turn off.  In most cases, I use a source meter (but that can cause its own problems).  Figure 3 in the bq51050EVM-764 shows a simple emulator using a power supply, a diode and some power resistors.  Changing the power supply voltage allows the system to respond to the voltage level and go through the charging cycle.  The power resistors allow the supply to always deliver current, as well as the bq51050B.  The diode prevents the bq51050B from trying to "charge the power supply".

Regards,

Dick

Hi Dick,

Thanks for your reply. as u mentioned, i tried with bigger coils, with a bigger coil 30mmx30mm 12.3uH , the voltage on RECT goes around 7V , and with coil 48mmx30mm 10.5uh RECT goes around 7.5 to 8V. also I noticed that with bigger coils, and when battery is around 3 then charging starts,and LED on CHG stays stable. but the battery is lower than that, the circuit behaves like not stable, connect and disconnect continuously.

I think the battery voltage is secondary and I think when good quality batteries are used.it might work properly.. Now our problem is, we are working on a wearable device, it shall not have a Wired USB for charging. so we have to relay on the wireless charging alone. also now primary problem is size. we thought 10mm x 30mm coil as a best fit for wearable. but now how can make the circuit work properly with the same coil.. we cant go for bigger coils.

please help on making the device work with same coil or similar same size coil. ,...and one more thing we have in mind. if we choose a multi coil TX Does this help in getting good coupling with small coil like the one we used.

Thank u

Chandra,

The goal of this exercise was to determine if it was the RX coil that was limiting your supply.  I think you did prove that.

I don't think a 3-coil TX will impact the results.  The multi-coil approach energizes one coil at a time in an attempt to find the best coupling.  It's not matching the TX coil to the RX coil.  Many of the wearable products use Qi-protocol, but are not necessarily Qi-certified.  

Look at a couple of our TI Designs:  TIDA-00415 and TIDA-00334 are good examples.  We find that using the smaller TX coils vastly improves the coupling which is what seems to be your issue.  The requirement is matching the RX coil capability to capture the magnetic field sent from the TX.  

Regards,

Dick