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more details for TIDA-00669

Other Parts Discussed in Thread: BQ51050B, TIDA-00669, BQ24040

Hi,

I'm Marco Pappalardo from Bycare Lab S.r.l.s. We are designing a device with a wireless power receiver.

We have designed a mixed wireless and USB-powered charger, taking the idea from TIDA-00669 reference design and BQ51050B datasheet.

I have four questions, I will explain my doubts below.

Reading the TIDA-00669 reference design: 

"The gauge is capable of self-correcting, accurately gauging and monitoring an alternate battery when connected to a compatible LI-ion or Li-Polymer battery with a range of 3.0V min to 4.2V max and a current capacity of 1000mAh to 2000mAh. The user must verify that the battery can be charged and discharged with the existing settings 500mAh charge rate or change the settings of this booster pack appropriately."

But in the BQ27421-G1A datasheet it is written that the "Recommended Sense Resistor input current" could be 2000 mA for "Long term RMS, average device utilization", 2500mA for "Peak RMS current, 10% device utilization" and 3500 mA maximum for "Peak pulsed current, 250 ms 1% device utilization". 

1) I have to use a 2200mAh Li-Ion battery, because I have absorption peaks of 2A, 250ms, due to the GSM module. Could I use it or not in my design? Looking to the reference it is not possible, but in the gauge datasheet it seems possible (due to the fact that I have only short-term peaks only during transmission and startup of GSM module).

2) Does the BQ27412-G1A allow to pass 2-2.1A current from SRX to BAT pin?

3) Using a 2200mAh battery would allow the system works but, maybe, the gauge will give me the full charge indication until the charge value goes under 2000mA?

In my mixed design I use a BQ51050B for wireless charging and a BQ24040 for USB charging, using the scheme in BQ51050B datasheet. I insert in my scheme the BQ27421-G1A as fuel gauge. I would like to use NTC monitoring not only for the BQ24040 but also for the correction of residual charge made by BQ27421-G1A. For this reason I've connected:

- TS pin of BQ24040 to the NTC

- BIN pin of BQ27421-G1A to the NTC through a 1.8-MΩ pullup resistor to VDD.

NTC is a 10kΩ thermistor.

4) Did I make it good or using two different connection to the NTC corrupt the reading of NTC resistance and the correct system operation?

Thank you for your response,

Marco

  • Marco,

    We will get back with the responses shortly. thanks!
    Gautham Ramachandran
    Applications Engineer.
  • Marco,
    Remember that each TI Design has specific parameters based on what is was designed to do. You can change any part of the TI Design to meet your requirements as long as it is with in the parts limits as set by the data sheet.

    1) I have to use a 2200mAh Li-Ion battery, because I have absorption peaks of 2A, 250ms, due to the GSM module. Could I use it or not in my design? Looking to the reference it is not possible, but in the gauge datasheet it seems possible (due to the fact that I have only short-term peaks only during transmission and startup of GSM module).
    Answer: The bq27421 can manage up to 8000mAh so your battery is well within spec. It can measure current up to 2500mA peak current, so your 2A draw form the GSM is not a problem. Yes this gauge will work fine for your application.

    2) Does the BQ27412-G1A allow to pass 2-2.1A current from SRX to BAT pin?
    Answer: Yes you can pass up to 3500mA for 250mS. The gauge does not current limit. The limit is based on the temperature rise on the internal resister. Your currents at or near 2A will not be a problem.

    3) Using a 2200mAh battery would allow the system works but, maybe, the gauge will give me the full charge indication until the charge value goes under 2000mA?
    Answer: the 2200mAh is a capacity and the gauge can properly gauge to 8000mAh. The charge or discharge current has nothing to do with capacity. The gauge can properly gauge your capacity and currents.

    4) Did I make it good or using two different connection to the NTC corrupt the reading of NTC resistance and the correct system operation?
    Answer: The bq24040 TS pin will source current that is needed to properly bias the 10K NTC. If you remove the battery the TS pin will go up to about 2V. The bq27421 BIN pin is a digital pin. When low detects a battery through the batteries internal 10K NTC, when the battery is removed it will go high and the BIN pin is pulled up through a 1.8M resister and will indicate no battery. This may not work as you indicate, there is a possibility that the 2V from the TS pin on the charger may hold the BIN pin on the gauge in the digital equivalent of floating, which may lock up the gauge. the gauge BIN high state is VBAT * 0.7, at the lowest VBAT voltage of 3.0V the BIN high threshold will be about 2.1V, the 2V from the charger will not be enough to pull it high or low.

    I hope this answers all of your questions. Let us know if you have anything else.

    Gordon Varney
    Sr. Systems Engineer
    BMS (Battery Management Solutions)
    Texas Instruments
  • Hi Gordon,

    first of all thank you for the fast answer, we've really appreciated it. 

    So taking into account the fact that it's better not to connect both TS and BIN pin to the NTC 10k resistor on the battery pack, which would be for you the best solution? 

    I mean, we could use the TS pin still connected to the NTC, while we can use a 10k resistor from BIN to Vss. We have a configuration where the battery pack is removable, but in the normal use of device we need it to remain connected, because its main purpose is to be a mobile device. So, we do not need the gauge battery insertion funcionality, because if the battery is removed the system will shut down.
    Conversely we could be in the need of using  TS/CTRL pin of BQ51050B to detect overheating during wireless charging. Is it possible to connect both TS pin and TS/CTRL pin to the NTC 10k resistor on battery pack? Or it will cause problems as in the case of my previous post?

    I would ask to you another question. I've seen that in BQ51050B datasheet, in typical application detailed design procedure the charging gap between receiver coil and charger coil (dz) is set to 3.4mm. I've seen the WPC v1.1 specifications, and it's written the gap could be up to 15mm (in the case signal losses being neglected). In our application we need this distance to be as far as possible. Now, I know that WPC v1.2 specifications allows "biggest" distances using a resonator coupling mode instead of a pure inductive one. But I know Wurth coils are not designed for it, because I've already talked to one of their field application engineer.

    My question is: how can I increase the distance to receiver and transmitter coil? Can I still meet the requirements of WPC v1.1 or WPC v1.2? Can I use the BQ51050B and coil in TIDA-00669 or do I have to chose another TI device and maybe another coil? Or with the same devices, which elements should I change in the design to make it works with the new distance?

    Thank you so much.

    Marco

  • Marco,

      In the past the IC that had a TS pin used an external bias voltage. Typically a 10k pull up to VCC and a 10k NTC to ground. The TS pin was just an ADC. Today the TS bias is pulled inside of the IC and then turned on periodically to measure the temperature of the NTC. This is the case with the bq51050B. That means that nothing else can be connected to the NTC except the one that is biasing the NTC. If you add a 10k pull up to the NTC then you will have 2 bias voltages and the temperature thresholds will be shifted then they wont work properly.

      My experience has been that the charger is the one that needs to measure the cell temperature. So the bq51050B needs to be the owner of TS. I think you are correct that if the battery is removed then you don't need to be gauging. Depending on the gauge you select, the problem I see is that if you remove the battery and then reinsert it, you may have to reload the gauge tables, to get the gauge to operate properly. If you don't have the recent gauge data collected, you will be loading old gauge data and that will mean that the gauge will be wrong. Some gauges will remember the data and some wont. Look closely at you gauge to see how it works.

    I have passed your second question on to the wireless charging guys. They should be able to answer your question based on the standards.

    I do know that the higher the Q of the coil the greater the distance you can get from the transmitter. The ideal coil has an inductance that uses only the inter-winding capacitance of the inductor and no external capacitor to be at resonance. Since this is nearly impossible select a coil that requires the lowest capacitor value possible. This may help but the transmitter is fixed so I don't know how much distance you can get and still meet the standard.

    Hopefully the wireless charging guys will be able to help you.

    Let me know if you need any more help.

      

     

  • Marco,
    I just remembered that you have two chargers, that means that you have two TS pins. I would use a simple SPDT mux IC so that you can switch between the two charges. Use the input voltage from one of the chargers so that when that charger is powered up the mux will switch the correct TS pin to the NTC.