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BQ24045: Battery NTC monitoring circuit for BQ24045 with BQ51051B (Qi-charging)

Carl Fredrik Leanderson
Prodigy 55 points
Part Number: BQ24045
Other Parts Discussed in Thread: BQ51051B, CSD75207W15, BQ51003, BQ51013B, BQ25170

Hi!

I am considering the combination of BQ24045 (to AC-adapter) with BQ51051B (Qi-charging) and am uncertain about the proper topology of the battery temperature monitoring circuit (NTC).

Based on BQ51051B DS, p. 24 (Figure 29, topology to the right in the figure, cf. excerpt attached), and the battery temperature requirements, we have chosen a certain 10k NTC with B=3435 (inside the battery). In our configuration, R_1 = 200ohm.

Hence, the battery NTC is currently monitored by the BQ51051B TS/CTRL pin

Now, I wish to add support for AC-adapter charging and am considering the schematics proposal on p.32 (Figure 37) of BQ51051B DS. In this schematics, the BQ24045 TS pin is connected directly to the NTC inside the battery, while the TS/CTRS of the BQ51051B is not connected to the battery NTC, but controlled from the host MCU.

Ideally, with the combination of BQ24045 and BQ51051B, we would like obtain the same temperature charging characteristics, regardless of which charger is used. Further, we would like to  to avoid  any SW implementation of temperature monitoring.

Is it possible to connect the TS output from both chargers to the battery NTC? If so, which topology would you recommend?

Alternatively, will the BQ51051B continue to monitor the battery temperature even in the case when BQ24045 is carrying out the battery charging? If so, can we count on the AD-EN output from BQ51051B to gate out the input voltage to BQ24045, should the temperature limits of the battery be exceeded? (provided that we use the CSD75207W15 back-back FET or equivalent)

Thanks and kind regards

/Carl Fredrik Leanderson

  • 0
    TI__Guru 67546 points

    Hi Carl

    Another configuration to look at is the BQ24045 + BQ51013B (or BQ51003).  The BQ24045 would always act as charger.  The BQ51013B would act as 5V supply during wireless charging, see data sheet figure 48.  This configuration will manage the NTC better.

  • 0 in reply to Bill Johns
    Prodigy 55 points

    Hi Bill!

    Many thanks for the diligent reply! I am sorry, but I could not find the schematics (figure 48).

    Is it in BQ24045 or BQ51003 datasheet or elsewhere?

    Concerning the TS/CTRL of BQ51051B - is it correct understanding that it will be active also when wireless charging is not active (though VBAT high enough), and, if so, will is conclusion about battery temperature affect AD_EN?

    Kind regards

    /CF

  • 0 in reply to Carl Fredrik Leanderson
    TI__Guru 67546 points

    Hi CF

    Sorry for confusion, I was looking at older version of datasheet.

    The figure would be in BQ51013B datasheet page 37, figure 9-11.  The same circuit will work for BQ51003.

    Carl Fredrik Leanderson said:
    Concerning the TS/CTRL of BQ51051B - is it correct understanding that it will be active also when wireless charging is not active (though VBAT high enough), and, if so, will is conclusion about battery temperature affect AD_EN?

    The TS/CTRL will not be powered without wireless power and AD high will disable wireless power.

  • 0 in reply to Bill Johns
    Prodigy 55 points

    Many thanks Bill!

    Concerning the TS pin on BQ24045 - would you please confirm that it is has similar implementation to BQ5105X, such that we can:

    1) use the CTRL functionality from host (high to send CHARGE COMPLETED, low to send CHARGE FAULT), and

    2) that we can use the NTC calculator tool to find values for R1 and R1/R3 (in schematics attached to previous question) to implement other than JEITA standard for battery charging curve vs temperature?

    (we need terminate the battery charging at 45degC)

    Kind regards

    /CF

  • 0 in reply to Carl Fredrik Leanderson
    TI__Guru 67546 points

    Hi CF

    The TS trip points are different between the two devices and 45C hot shutdown will be difficult, have see issues before.

    Recommend looking at the BQ25170 this device TS is 45C friendly and easier to set up.

    The BQ25170 will work work well with BQ51013B or BQ51003 as mentioned above.