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BQ51050B: Wireless charge adapter pin AD connection

Hafiz Haja
Intellectual 490 points
Part Number: BQ51050B

Hi,

I am designing a wireless charger based power receiver module which uses BQ51050B as wireless charger. PCB has been fabricated. While testing when cross verifying schematics, I found that I have missed the connection of AD pin short to GND. In datasheet it is recommended to connect this pin to GND for wireless charging. What will be the impact if this pin is left floating?. Since PCB is fabricated only way to provide short to GND is taking jumper wire. What is the internal logic of this pin. Should this pin must be connected to GND for wireless charging to initiate.

Regards

Hafiz

  • 0
    TI__Guru* 75656 points
    Hi Hafiz
    Floating the AD would be bad. It will detect the adapter is present and disable wireless charging.
    If a 1uF capacitor is connected to the pin that will be enough to prevent pin from floating high.
    Leakeage current out of the pin will cause it go pull high and trip the Adapter detect circuit. Adding a capacitor, connecting to ground or pulling low will prevent problems with leakage current.
  • 0 in reply to Bill Johns
    Intellectual 490 points

    Hi Bill,

    I have shorted the AD pin to GND. Now  i am testing  wireless charging using the transmitter F303W Fast Wireless Charger from Spigen in order charge my 3.7V (4.2V max) Li-Ion battery via BQ51050B. Transmitter is trying to ping the receiver, but charging is not happening. I have probed the receiver coil input voltage and rectifier input voltage. Attached the probed waveform for your reference. Measured inductance of receiver coil is 27uH and is printed on flex p cb. The received voltage level is reaching 30V peak. What will be the reason?. This may cause the charger IC to get damaged, right?

  • 0 in reply to Hafiz Haja
    Intellectual 490 points
    Hi,

    Is there anyone with a resolution for this problem?
  • 0 in reply to Hafiz Haja
    TI__Guru* 75656 points
    Hi
    What is the tuning of your RX coil, this would be the series capacitors (Cs or C1) also value of RX coil in the case on the TX (Ls')?
    What is the coil to coil distance?

    27uH above could be the free air value of the coil, typical spec but not Ls' value. This is a good value for a small coil.
  • 0 in reply to Bill Johns
    Intellectual 490 points
    Hi,
    Yes 27uH is the free air coil inductance. The tuning value for Cs is 150nF (25V rating) and Ls' is around 31uH. Coil to coil distance is around 3 mm. For initial wireless charging testing we placed the coil directly above the spigen F303W power transmitter. Should there be any shielding between Rx coil and spigen TX coil?
  • 0 in reply to Hafiz Haja
    TI__Guru* 75656 points
    Hi
    The Cs value should be about 80nF for 100kHz resonance point with 31uH.
    Coil to Coil distance looks OK
    I am guessing your RX coil is about 20mm in diameter.

    Recommend trying another transmitter, take a look at the TYLT VU Solo.
  • 0 in reply to Bill Johns
    Intellectual 490 points
    Hi

    The RX coil diameter is 40mm with trace thickness of 0.81mm and space between space of 0.2mm printed on Polyimide PCB. I will try changing the Cs capacitance. But still doubt is there regarding 30V RX input voltage. TX is verified using evaluation module

    Regards
    Hafiz
  • 0 in reply to Hafiz Haja
    Intellectual 490 points
    Hi,

    What may be reason of receiver input voltage reaching above 30V?. We are running out of time for completing this project. Kindly support.

    Regards
    Hafiz
  • 0 in reply to Bill Johns
    Intellectual 490 points
    Hi Bills,
    I have changed the Cs value to around 80nF and now the CHG# LED is glowing for me. Battery charging has been initiated. I am using a 200mah Li-Ion thin film battery with recommended charge rate of 1C (200mA). But for the improved life cycle of the battery, we need maximum 160mA battery threshold current. Ibulk is set to be 800mA by selecting Rilim = R1 + Rfod = 390 ohm. Now in order to set the upper termination threshold to 160mA (~20% of 800mA) the termination resistor chosen is 4.7 k ohm. But while the battery is charging the charging current is increasing beyond 250mA when the RX and TX coils are correctly aligned. Is there any problem in the calculations made? Kindly provide feedback.

    Regards
    Hafiz
  • 0 in reply to Hafiz Haja
    TI__Guru* 75656 points
    Hi Hafiz
    To configure the BQ51050B for 160mA charging current set R1 + Rfod = 1.96k ohm. Set R1 to about 100 ohms and Rfod to about 1.8k ohm. See equation 1 in datasheet.
    To configure the termination current recommend 20% which would be 4.8k see equation 2 in data sheet. You are using 4.7k this will work. At low charge current the termination accuracy is low and do not recommend terminating below 30mA.
  • 0 in reply to Bill Johns
    Intellectual 490 points

    Hi,

    Thanks for your support. This will help completing my design.

    Regards

    Hafiz

  • 0 in reply to Bill Johns
    Intellectual 490 points
    Hi
    I have put 330 ohm at R1 and 1.5k ohm at Rfod. Also for Iterm I have put 5.6k ohm (>40mA). Ibat after fast charge mode is reducing and keep on reducing. No charge termination is happening even if Ibat reaches 10mA. What may be the reason
  • 0 in reply to Hafiz Haja
    TI__Guru* 75656 points
    Hi
    The ILIM pin is a current that is proportional to output current.
    The TERM pin is a fixed current that will set the point where termination occurs.
    ILIM and TERM will work together for termination. Try comparing the voltage between the two pins.
  • 0 in reply to Bill Johns
    TI__Guru* 75656 points
    Hi Hafiz
    I have split the BQ29700 post off as a separate thread. The device is supported by another group and I am not the expert on it.
    You should have received and email. Also changed the Title to better reflect the content.
  • 0 in reply to Bill Johns
    TI__Guru* 75656 points
    We have the AD question closed along with FOD setting.