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BQ51013B: Output issue in EN1=0, EN2=1 case
Part Number: BQ51013B
Hi guys. I am part of a college engineering team developing a product that utilizes TI's BQ51013B chip to provide a wireless charging solution. The application requires charging of two lithium Ion 14430 batteries of 600 mA each and they both draw about 300-500 mA.I am having difficulty sizing the comm/boot capacitors exactly for our application. We are using a coil with the following characteristics:
Inductance +/-2%, @ 200kHz (uH) = 11.6DCR +/- 2% (mOhm) = 520ESR +/- 2%(mOhm) = 635Q Factor = 23ProjectSchematic.pdf
I have attached a schematic as a pdf format based on the Datasheet. I would appreciate any feedback and review.
An important question I had is how far can the coil be placed from the chip itself and is it possible to place it at a longer distance of about 10-15 cms somehow?
10cm to 15cm is a little too far for this system. Typical coil to coil distance is 3mm to 5mm.
The TX sends out a digital ping, this is full wave rectified to produce a voltage at RECT pin. The voltage needs to exceed UVLO 2.7V to start operation.
Schematic looks OK.
Bill Johns, Applications Engineer
Texas Instruments Inc
For more information on Battery Charger Solutions see Link
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In reply to Bill Johns:
Thank you very much for your prompt assistance Bill. I will try this out.
Electrical Engineering Technologist
Applied Research Division
Algonquin College, Ottawa Ontario
Our PCB's arrived and we tested them. They seem to be recognized by transmitters but the output voltage of the board is just under 1.7 volts. Would there possibly any specific reason for this? How would I go about testing/diagnosing the problem?
Thanks for you time.
In reply to Kuwar Dalal:
Are you seeing the 1.7V at RECT pin?
This is an indication the coupling and gain of coil is low, possibly tuning is an issue.
I will check the voltage on the RECT pin and get back ASAP. I was only able to 1.7 on the OUT pin. I also just noticed that I put the RECT capacitor C3 after the Ros resistor. Could that possibly be an issue?
Is the capacitor C3 or C17? C17 in above schematic is not a problem. But you do need a large bulk capacitor on RECT pin.
It is odd that you are getting 1.7V on OUT. The output is not enabled until the voltage on RECT is at target.
I misread my schematic, I do have a bulk capacitor as the datashet recommends on C3.
I did some further tests today. I chose a random qi wireless transmitter and measured voltages at each pin with strange results. The signal across the coil looks like this:
A close up looks like this:
The Voltage at the Rect pin is between 3.5 volts to 5.5 volts sometimes and looks like this:
The voltage on the output is still between 1.4 to 1.8 volts although I did get 2 volts fiddling with the placement. The PCB looks like this:
We are using the following receiver coil: https://www.digikey.ca/product-detail/en/molex/1461791001/WM15000-ND/6159262
I have to try different coils to see if anything else works. The datasheet walks through the calculation of C1 and C2 for tuning and says " For this application, the selected coil inductance, Ls, is 11 μH and the Ls' is 16 μH with a DC resistance of 191 mΩ." What coil is used here that its referring to. Could this still be a gain/tuning issue?
Appreciate all the help Bill!
The Coil and tuning look OK.
Can you take closer look at RECT voltage vs OUT voltage. Should see the control packets at start up and during power transfer.
What load are you testing with?
"What load are you testing with?"
I tried with just a plain red LED which seems to light up intermittently. I am seeing decent gain and coupling in the coil, so the tuning did seem OK.
I also noticed that I tied the LED to the RECT pin instead of the out pin but this wouldn't cause an issue like this would it?
From the test and troubleshoot manual from TI I was able to find the following:
I am only getting about 5 volts at the RECT. I tried some other coils as well.
The following pictures are form the scope:
Vout on Start up:
Vrect on startup:
What could cause the voltage on Vrect pin to not be sufficient?
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