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Original question:

BQ51003: FOD Calibration

BQ51003: Rx in range of Tx status?

Paul Gancitano
Prodigy 95 points
Part Number: BQ51003
Other Parts Discussed in Thread: BQ51020

We are using the BQ51003 as a wireless Rx for a medical device. This feeds 5V into a battery charger IC for a lithium-ion battery. The Tx is an NXP NXQ1TXH5/101J.

We have a microcontroller tied to the EN1/EN2 pins, and we are monitoring battery voltage. When battery voltage reaches the charge threshold, the microcontroller pulls these pins HIGH to send a "charge complete" 0x01 packet to the Tx to terminate power transfer. However, we still need a way to be aware of whether the device is still docked on the charger, or if it has been removed. If it has been removed, it must enter a "low-power" state.

Right now, the only way we can think of doing this is occasionally pulling EN1 LOW (every 10s or so) to see if a Tx connection is established; if not, the device must be out of range and therefore undocked. However we want to monitor this in a more efficient manner. As I understand, the Tx will continue to send pings for an Rx in range, to which the Rx will respond with a 0x01 if EN1/EN2 are HIGH. Is there any way to utilize the BQ51003's other pins to monitor if it is receiving connectivity pings from a Tx, indicating that it is in range of a Tx, even though it is responding with 0x01?

  • 0
    TI__Guru* 75926 points

    Hello

    It may be possible to monitor the RECT pin and look for a spike the voltage.  The ping that TX send out to check on the RX will cause the RECT voltage to spike up.  The ping will be low power and should not increase to UVLO and power the device.

    Often the TX will send a longer ping to power the RX so it can reply.  When it sends this and depend on the TX and not sure when NXP will do this.

  • 0 in reply to Bill Johns
    Prodigy 95 points

    Thanks Bill. It looks like the RECT pin pulses to ~12V every 5s when it is in range of the NXP charger.

    We are considering switching to the TI BQ51020 because this chip has a PAD DETECT pin. However, it is more expensive and would require a re-design on our part. Does the Pad Detect operate exactly the same way that the RECT pin does on this chip? Would it be beneficial to switch to the BQ51020 to utilize this feature? Do you have any advice on critical functionality between the two chips?

    Thanks for the help.

  • 0 in reply to Paul Gancitano
    TI__Guru* 75926 points

    Hello

    The BQ51020 pad detect feature will use pulses on RECT also.  The pulse will charge and external capacitor with a long discharge time, compairator monitors the pin then drives pad det output.

    Can probably be implemented on the BQ51003 with external circuit if you have an MCU to work with.

  • 0 in reply to Bill Johns
    Prodigy 95 points

    Bill, It looks like the RECT pin only responds with a pulse when a digital ping is sent. When the Rx is held in EPT01, the NXP Tx will continue to send analog pings every 400 ms, and a digital ping every 5s. From another E2E post:

    "There are two different approaches the TX can take.  The TX will continue to check to see if the RX has been removed by sending a "ping" every 400ms-500ms.

     If the ping is "analog", the TX is checking to see if the RX has been removed yet.  It will continue to send this ping until it senses the RX has been removed.  Once removed, it will still send the pings waiting for another RX to be placed on the system.  Then, it will power up that system as a new system.

    If the pin is "digital", there is enough power transferred to turn on the RX.  In this case, the bq5105xB will respond with another end of charge signal."

    Is there a way we can look for the analog pings on the BQ51003? We need the system to respond faster than ~5s when the device is removed from the charger.

    Is it possible to contact you directly about this? Unfortunately this is a high-priority issue and it would be more efficient to speak with you directly. 

  • 0 in reply to Paul Gancitano
    TI__Guru* 75926 points

    I will contact you