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CCS/BQ51050B: BQ51050 : How to choose RX coil and TX coil values

Mike Jaber
Expert 1110 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ51010B, BQ500212A

Tool/software: Code Composer Studio

Hello,

We are actually working on a project and we would like to add a wireless charging functionality. We have chosen the BQ51050BRHLR receveir circuit. However we are new with these wireless charging ICs. We have three main questions :

1) We have checked the BQ51050BRHLR datasheet and we still have doubts how to choose the receiver coil inductance value. I mean do we have to fix a "random" value for the inductance ? Moreover in the datasheet, they talk about Ls and L's. Which one correponds to the receiver coil inductance we have to buy and connect between AC1 and AC2 ? Therefore when we have to chose a receiver coil, do we have to choose it according to its inductance value or DC resistance or both ? We by the way designed the circuit for a 530 mA charging current and the VBAT is a 3.7 V Li-Po battery. 

2) So here is below our scheme. We don't know if it's correct and if something is missing without taking account of the missing RX coil.

3) Finally, since we just talked about the receiver circuit, we need a transmitter circuit. Do you recommend any TI transmitter circuit which would be suitable with the BQ51050BRHLR circuit ? In fact we would like if it exists, a board integrating already the transmitter circuit with all the necessary circuits around, so we just have to put the RX coil near the TX coil to start the wireless charging. And how should be the TX coil value comparing to the RX coil one ?

Thank you very much.

Best regards,

Mike

  • 0
    TI__Guru 71166 points

    Hello Mike

    Do you want to keep this post or the BQ51010B?

    Coil -- try using the coil from Evaluation board or similar -- The Wurth 760 308 103 202 would be good to start with, Ls = 12uH and coil is 48mm X 32mm.

    Ls vs Ls' -- For a larger coil (48mm X 32mm) Ls of 12uH is good but if coil is smaller (15mm round) us higher Ls of 30uh to 40uh.  The series resonant capacitor are missing on schematic and with be used to tune the coil using Ls' value.  See data sheet for Ls' measurement and tuning.

    Schematic -- has a couple of problems, see Figure 32 in data sheet for typical application.  Series resonant capacitors (C1), ILIM and FOD resistors need to be re-wired. 

    Transmitter (TX) -- The TYLT VU SOLO is a TI based design that is available.

  • 0 in reply to Bill Johns
    Expert 1110 points

    Hi Bill,

    Thank you for your response.

    So here is our scheme now after some corrections. I don't know if something is still missing, but I think we fixed the connections problems you mentionned in the last post.

    We by the way noticed in the datasheet on Fig.32 (p 28) a Ros resistor connected to RECT pin. We didn't find a description of this resistor in the datasheet and that's why it's still missing in the scheme above. Is this resistor mandatory ? And what value to choose for it ? 

    Concerning the TX transmitter (TYLT VU SOLO), I have checked it on the net. Are you sure it could be suitable with the BQ51050 circuit ? And is there something less expansive, I mean a TI board for example where we just have to put the RX coil near to it, and start the wireless charging ?

    Finally as you recommend us we have chosen a 12 uH Rx coil. And for C1 and C2 calculation we took Ls' 16 uH as mentionned in the datasheet. Is this right ? 

    Thank you.

    Regards,

    Mike

  • 0 in reply to Mike Jaber
    TI__Guru 71166 points

    Mike

    Need to connect the EP-thermal pad (pin 21) to ground plane for thermal management. 

    "We by the way noticed in the datasheet on Fig.32 (p 28) a Ros resistor connected to RECT pin. Is this resistor mandatory ? And what value to choose for it ? " -- Bill J - This is used for FOD Tuning, need to add it.  Cannot connect RECT directly to FOD pin.  Recommend value of 20k to start with.

    "Concerning the TX transmitter (TYLT VU SOLO), I have checked it on the net. Are you sure it could be suitable with the BQ51050 circuit ? And is there something less expansive, I mean a TI board for example where we just have to put the RX coil near to it, and start the wireless charging ?" -- Bill J - Yes it is suitable, built using the TI BQ500212A.  If you encounter problems I know what the transmitter is doing, this will make it easier.

    "Finally as you recommend us we have chosen a 12 uH Rx coil. And for C1 and C2 calculation we took Ls' 16 uH as mentionned in the datasheet. Is this right ?" -- Bill J -- Yes this looks good

  • 0 in reply to Bill Johns
    Expert 1110 points

    Hi Bill,

    Thank you very much for your reply. 

    Once we test the BQ51050 with the TYLT VU SOLO, I will repost here if we encounter some problems.

    Best regards,

    Mike

  • 0 in reply to Bill Johns
    Expert 1110 points

    Hi Bill,

    We would like to buy the TI based design TYLT VU SOLO. Can you provid us a link where to buy it on suppliers like mouser, digikey... 

    Thank you,

    Regards,

    Mike

    TYLT VU SOLO
  • 0 in reply to Mike Jaber
    TI__Guru 71166 points

    Hi Mike

    They are available on Amazon.

  • 0 in reply to Bill Johns
    Expert 1110 points

    Hi Bill,

    Thank you for your response.

    Regards,

    Mike