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Original question:

BQ51003: Calibrated transmitter for FOD calibration

BQ51003: FOD Calibration

Paul Gancitano
Prodigy 95 points
Part Number: BQ51003

Similar to another user, I cannot calibrate the FOD, because the calibrated Qi transmitter in the FOD calibration tool is no longer available. I am looking for alternate ways to calibrate FOD using an off-the-shelf Qi transmitter.

Application detail: Our BQ51003 Qi receiver is fed into an NXP MC34673AEPR2 charging IC. As the battery nears end-of-charge and charge current into the battery is reduced, the battery (which is directly behind the coil) gets very hot. I think it is absorbing energy from the Qi transmitter and not properly recognized as a foreign object. 

  • 0
    TI__Mastermind 19195 points

    Hi Paul,

    Have you tried putting some shielding material between coil and battery? Check out our FAQ here on RX overheating: https://e2e.ti.com/support/power-management/f/196/t/905835

    Best,

  • 0 in reply to Nick Brylski
    Prodigy 95 points

    Hi Nick,

    Yes, when the battery is not located in the field of the Tx, it does not become hot (as suggested by the forum you posted). This tells me the C1/C2 capacitors are tuned correctly.

    We placed a ferrite sheet between the coil and the battery, and it does bring the temperature down, but does not eliminate the problem. What we're seeing happen is when the battery goes into trickle-charge from the charger IC (NXP part), the battery quickly heats up, and the BQ51003 does not communicate to the Tx that that charge should be terminated. It's as if the energy that is not being passed to the battery by the charger IC is just sunk into the foreign object, but the BQ51003 never communicates to the Tx that it should terminate the charge. So the Tx continues to emit, as the temperature rises more and more, beyond safe limits for the battery.

    We have lowered the charge current by adjusting R1 in the schematic. I have also tried manipulating R_FOD without success so I am not totally sure of the relationship between this resistor setpoint and how the Rx would communicate to the Tx if a foreign object was present.

    Any advice you have on a) adjusting FOD so that this phenomenon is mitigated, or b) suggesting a better way to interface the BQ51003 and Battery charger IC?

    Thanks again.

  • 0 in reply to Paul Gancitano
    Prodigy 95 points

    Nick: As a follow up question, under what circumstance would I expect the BQ51003 to send a "charge complete" packet to the Tx? Am I waiting for this to happen when in reality the chip is not configured in this way? I have yet to observe my device disconnect Qi power transfer, even when induced current is reduced to a trickle (< 10 mA), but maybe this is expected behavior. If the Rx is expected to disconnect power transfer, under what circumstance would the charge re-initialize?

  • 0 in reply to Paul Gancitano
    TI__Mastermind 19195 points

    Hi Paul,

    Are you able to raise the termination current on the battery charger? <10mA is quite low. We don't think FOD calibration would help here.

    The BQ51003 during light load will increase V-RECT voltage to about 7V.  This will require a larger AC field in some coil configurations.

    Will be looking into your other questions.

    Best,

  • 0 in reply to Nick Brylski
    TI__Mastermind 19195 points

    The BQ51003 does not detect charge complete and send a command to the TX to turn off.  This would be a Charge Complete Packet (EPT01).  If EN1 and EN2 are pulled high the BQ51003 will send a EPT01 to TX.  This needs to be managed by an MCU. 

    Best,

  • 0 in reply to Nick Brylski
    Prodigy 95 points

    Thanks Nick. We will plan to do that. After the EPT01 is sent to the Tx, does the Rx remain powered but no voltage is present on the OUT pins? We're trying to power a "charge complete" LED but if nothing is present on OUT, can we pull power from RECT or another I/O on the BQ51003?

    Would the Tx attempt to re-initialize a charge? Or would this only happen after the BQ51003 and coil are removed from the TX field and placed back again?

  • 0 in reply to Paul Gancitano
    TI__Mastermind 19195 points

    Hi Paul,

    After the EPT01 is sent to the Tx, does the Rx remain powered but no voltage is present on the OUT pins? ---(Nick) – No when TX is off RX is off

    We're trying to power a "charge complete" LED but if nothing is present on OUT, can we pull power from RECT or another I/O on the BQ51003?----(Nick)—No, the Pull Up would need to come from battery.  With TX off no voltage at RECT.

    Would the Tx attempt to re-initialize a charge?---(Nick) – not if EN1 / EN2 are high, RX will reply with EPT01. 

     Or would this only happen after the BQ51003 and coil are removed from the TX field and placed back again?---(Nick) – Many TX will ping the RX to see if they need more power. But this depends on the TX when it will check back with RX. 

    Best,