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connection problem with bq500211A and BQ51050B. Maybe communication?

Manuel Walter
Prodigy 130 points
Other Parts Discussed in Thread: BQ500211A

Hello,

a the moment I'm trying to verify a power transfer between two boards with the ICs mentioned above. The designed receiver works fine with the purchased bq500211AEVM. But if I put the receiver on the self designed Transmitter board (the low-cost schematic of the datasheet was used as a template), the LED on the receiver which should indicate a charging is not glowing. The transmitter seems to detect  the receiver correctly. When I place the receiver on it, the LED connected to BUZ_DC is on for a about half a second or something.

Do you have any suggestions how to detect the problem? When exactly is the BUZ_DC triggerd? Just after detecting a receiver coil or after the successful identification of a receiver with communication packages? In the datasheet it says: "outputs a pulse when charging begins".

Kind Regars

Manuel

  • 0
    Prodigy 130 points

    okay... i found a solution by myself, but I really need help understanding it. As mentioned above I had the bq500211AEVM as a reference. The coils I tried my own board with, where from wuerth electronics type 760308105. The coil used in the EVM is 760308111, so to say, mine is für qi-standard transmitter type A5 and the EVM was qi-standard type A11. Because of not getting a connection I un-soldered the EVM-coil and used it in my board and well, receiver indicated the charging state.

    What is the reason for that?

    Both coils have an inductance of 6,3uF and approximately the same outer diameter. The obvious difference ist the magnetic attractor, which is used for the A5 coil but is missing in the A11 coil, althoug the qi-standard says the A11 transmitter to be one with guided positioning. The other difference I could find by studying the datasheets of the coils, is a different Q-factor. The A5 has 55 and the A11 has 80. I will measure and verify that tomorrow.

    The next confusing discovery was, that the EVM however worked with the A5 coil. Not as good as with A11 but it worked. 

    What about the material under EVM coil? There is some kind of elastic tape and a metal plate between the coil and the pcb. Do the have any special functionality?

    I would be really happy if you could help me finding an explanation and maybe a solution how to use A5 coils with my board. 

    Thank you very much

    Manuel

  • 0 in reply to Manuel Walter
    TI__Guru 69136 points

    The A5 TX coil with a magnet or A11 with no magnet should not be a factor.  It will not change the tuning of the bq500211A TX (400nF low ESR C, COG).  

    But the magnet could change the tuning of the RX coil, it will bias the BH curve and increase the risk of saturation.

     

    But if you are using the bq51050EVM the coil is OK.

    When exactly is the BUZ_DC triggerd? --- After valid ss/id/config packet

    It sounds like you are having communications problems between RX and TX.  Compare the COMM+ signal with EVM.  Verify that COMM+ has a 1.5V DC bias on it.

  • 0 in reply to Bill Johns
    Prodigy 130 points

    Thank you very much for your fast reply. 

    The receiver coil I'm using is wuerth electronics type 760308201, the same you are using in the BQ51050BEVM. 

    I'm not really sure whether it is a communication problem. Increasing the size of the resonant caps on the receiver made a charging possible althoug using A5 coil with our board. What appears to be strange is, that a slight decentralisation of the rx coil on the tx coil is needed for that.

    Unfortunately the connection between the rx and the tx is very weak, although having the better working coil A11. The maximum charging current is about 400mA and the connection aborts if the coil position changes slightly. Also the charging only works with a distance of 2mm between the tx and the rx coil.

    Furthermore I discovered a noisy supply voltage from the LDO to the bq500211A. It seems that this voltage is affecting the PWM.

    I couldn't measure the bias today, but just in case it isn't 1,5V, what adjustments could I make to increase the communication quality? Should I increase the loadmodulation caps on the receiver from 22nF up to 60? Or should I modify the Resistor R6 on the communication wire?

    Thanks again

    Manuel

    Edit:

    Today I could verify the bias of 1,5V on the comm+ signal of the TX. But I realized that the amplitude of the signal is lower than the one on the EVM board. This made me discover, that my version of the tx is not adjusting the oparating frequency. It is kept constant at 205kHz, almost 206kHz, the maximum limit which is possible within the qi specifications. The transmitter is not reducing the frequency, althoug the receiver is only able to charge with 300mA but should charge with 1A. Is there any reason why the transmitter is not adjusting his oparating frequency?

    Could communication problems affect the transmitter to constantly apply a power signal but not adjust it? I don't think it is a problem of saturation because our receiver works fine with the A5 coil as long as it is used on your bq500211AEVM and not on our self designed board.

    I hope I'm not getting on your nerves, but solving this problem would realy mean a lot to me.

    thanks again.

    Manuel

  • 0 in reply to Manuel Walter
    Prodigy 130 points

    Are there any advice?

    Kind regards

    Manuel

  • 0 in reply to Manuel Walter
    TI__Guru 69136 points

    The schematic you have used is from bq500211A data sheet figure 8.

     

    “The designed receiver works fine with the purchased bq500211AEVM. But if I put the receiver on the self designed Transmitter board (the low-cost schematic of the datasheet was used as a template),”

     

    What is the connection of Pin 46 of bq500211A?

    It should be tied to 3.3V not ground.

    This will cause the DPL function to operate and unit to go to 205kHz.

  • 0 in reply to Bill Johns
    Prodigy 130 points

    Thank you very much Bill!

    You are right... Pin 46 is set to GND, just like in the schematic of the low cost version.

    So how du I connect it correct? 76.8k and 10k parallel to 4,7nF like in the datasheet of bq500211A or 15.4k and 2k parallel to 4,7nF like in the schematic of the EVM?

    Kind regards

    Manuel

  • 0 in reply to Manuel Walter
    TI__Guru 69136 points

    Pin 46 need to be greater than 400mV.

    It can be pulled up to 3.3V (V33D or V33A).

    The standard divider network will work also, 15.4k and 2K or 76.8k and 10k.  Filter cap of 4.7nF would be OK.

  • 0 in reply to Bill Johns
    Prodigy 130 points

    Ok, I'll change that. Thank you very much so far.  Are there any other necessary changes regarding to the low-cost schematic of the datasheet?

    Manuel

  • 0 in reply to Manuel Walter
    Prodigy 130 points

    What about ISENSE (pin 42)? It has a pin description similar to pin 46 (VSENSE). In the schematic it says "Current Sensing is Optional but Provides Roadmap to WPC1.1". At the moment I have pin 42 tied to ground, too. Will this cause the transmitter to be less powerful just as it is at the momen?

    Thank you in advance

    Manuel

  • 0 in reply to Manuel Walter
    TI__Guru 69136 points

    Ground for I_Sense is OK, Pin 42

  • 0 in reply to Bill Johns
    Prodigy 130 points

    Ok, thank you for all your efforts!

    Kind regards 

    Manuel