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BQ500511A: Difference between A and non-A version bq500511(A)/bq50002(A) combination

Wout Geeurickx
Prodigy 235 points
Part Number: BQ500511A
Other Parts Discussed in Thread: BQ50002A, BQ500511, BQ50002, BQ25100, BQ51003

Hi,

I am struggling to find the difference between the bq500511/bq50002 and the bq500511A/bq50002A combination.

The only thing I seem to find in the datasheet of the bq500511(A) is that the bq500511A has "Improved Demodulation Algorithms Provide Robust Communication in Noisy Environments". For the bq50002(A) I found this sentence missing from the bq50002 version: "When paired with the bq500511A the offset in the bq50002A current sense amplifier is dynamically compensated, which allows accurate FOD performance".

Am I correct in assuming the A version of the combo is more robust and will have better performance, or is this only situational?

The main reason why I am asking this question is because we have an issue with our TX charger based on the reference designs with the non-A combination. With all casing and realistic spacing between the coils, charging seems to start but after 20-40 seconds, LED_B either starts blinking slowly (LED option 1, so DPL I am assuming) or is constant on (what is the best way to debug source of fault?). When we remove some material and hence decrease the distance between the coils, the charger seems to work fine (LED_A remains blinking). It seems that we are operating at the edge for the current configuration. I was wondering if using the A combination, we would move more towards the safe end of the edge.

Thanks!

Wout

  • 0
    TI__Guru 65846 points
    If you have a blinking LED_B this could be DPL or FOD.
    DPL would be caused by a low 5V supply, check with an oscope or DVM, if it is low try to increase.
    FOD test by disabling FOD fault by pulling FOD_THR Pin 35 to 3V.

    BQ500511A / BQ50002A combination is an improved version of the device, better communication and FOD performance. The two devices need to be used together, no mix A and non-A. The non-A version is NRND and should not be used.

    Also if your circuit is having trouble communicating this would cause the 20 to 40 seconds to start charging. But a communication problem could be caused by several problems and is difficult to troubleshoot.
  • 0 in reply to Bill Johns
    Prodigy 235 points

    Hi Bill,

    Thank you for your response.

    The blinking LED_B now only happens marginally, most of the times the LED is constant on. FOD is already turned off by pulling FOD_THR high. After some debugging we found that the TX Overtemperature is at the cause of this. We removed the NTC (so TSENSE is pulled-up, always on) and this fixed the "issue". Of course now we have a device that keeps heating up. I measured temperatures up to 90°C and still increasing with a IR camera. At the RX side, we only charge a battery at 4.2V, 60mA (0.25W). However, we measured the input current for the TX and this averaged at around 350mA (1.75W). Of course there is some additional loss (charging is done using the bq25100 after the bq51003 RX), but this seems a very low efficiency.

    The distance between the coils is 1.8mm with 1.4mm Liquid Fotoreactive Acrylate in between. The TX coil is WT151512-22F2-ID and the RX coil is WR121210-27M8-ID. The tuning caps on the TX side are 368nF, on the RX side Cs = 288nF and Cd = 2.8nF.

    Do you have any suggestions to increase efficiency and effectively decrease the temperature increase (apart from fine-tuning the matching)?

    Thanks!

    Wout

  • 0 in reply to Wout Geeurickx
    TI__Guru 65846 points
    Check the operating freq, this will give some indication efficiency of power transfer. Lowest freq and highest gain is 110kHz and would expect you to be near 150kHz.
    The L value of RX coil is on the low side about 8.5uH we have used the WR222230-26M8 (26uH) on other designs.
  • 0 in reply to Bill Johns
    Prodigy 235 points
    Hi Bill,

    I am seeing an operating frequency which is varying between 120 and 130kHz. How can I bring this back to the optimal frequency of 110kHz, or is this purely done by tuning? Why do you expect our frequency to be around 150kHz?
    The reason for the RX coil is purely based on dimensions of the coil. We need a very small product and this coil has a small diameter and most importantly a very small thickness. I know we are shooting ourselves in the foot with this one, but it is kind of forced upon us by our client.

    Best regards,
    Wout
  • 0 in reply to Wout Geeurickx
    TI__Guru 65846 points
    Hi Wout
    The operating freq is an indication of performance, tuning, coil behavior and other factors. If you are running at or near max operating point 110kHz something is wrong and 120kHz to 130kHz is not good. This is a high operating point with low margin.

    You want to set things up so you have some margin of coil to coil off-set, low input voltage and other things that will reduce efficiency. Operating freq about 150kHz.
  • 0 in reply to Bill Johns
    Prodigy 235 points
    Hi Bill,

    Is this the expected frequency when there is no RX in the neighborhood? Because I was under the impression that the frequency is regulated based on the power requirements. If that is not the case, and the frequency should be close to 150kHz during normal operation, why is the frequency range then defined between 100-200kHz?

    Best regards,
    Wout
  • 0 in reply to Wout Geeurickx
    TI__Guru 65846 points
    If no RX present the unit will be in a standby mode and TX will ping the coil every 500mS to check for RX. Ping freq is 175kHz for about 80mS.
    When the RX is in place and power transfer has started the freq will vary with load. Light load will have a higher freq and heavy load will have a lower freq.
    The one thing about a light load is the voltage at RECT (RX) is increased and this will cause the operating freq to be lower than expected.