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BQ51051B: switch Vout between battery and wireless power

Part Number: BQ51051B
Other Parts Discussed in Thread: BQ51013B, CC3200MOD, CC3200

Hi all,

I'm developing a low power Iot device, and I'd like to power it using wireless power (no wired power supply). I found the BQ51051B as possible solution but I need some claryfication on its use and in general about the wireless charge tecnology. My scenario is the following:

1) Device near the wireless power transmitter: the wireless power receiver inside the device should give power to the device and at the same time recharge the battery device.

2) Device far the wireless power transmitter: the device is powered only by the inside battery.

In the schematics I found, the BQ51051B is used to recharge only the battery but not to power other circuits, where I can found a correct schematics ? should be BQ51051B able to give an VOut pin when I can switch power between battery power and wireless power source?

Thanks!

Riccardo

  • Hi Riccardo
    Using some of the output from charger to power the battery is possible. But this would depend on the system details, charge current vs current used for system. Also how would a deeply discharge battery support the system, charge current would be limited until voltage increases above 3V.

    Other system configuration are also possible, the bq51013B with 5V output supplying battery charger and system.
  • Hi Bill,

    thanks for your reply. The device I'm developing will based on the cc3200mod with a rgb led, a push button and some sensor like bme280, and all the system will works in the lowest power mode, always connected using wifi beacon packet from the access point and sleeping between them.

    The device will stay on the charge box (with the wireless power transmitter) for the longest time, and sometimes will be detached to use the in mobility (in this case the battery should provide the power), so the wireless power system priority is to mainly power the device, and the remaning power can recharge the battery (no time limit). I'd like to know if TI provides any integrated solution on chip to manage a situation like this in transparent manner about the switch between wireless powet source and battery, and about wireless power supplying and battery recharge when the device stays on the charge box.

    Thanks!

    Riccardo

  • How large a battery will you have in the unit?
    What is the charge current?
    What will the system load look like, average and max load?

    I am not sure the bq5105X is the best fit. It has a 10 hr safety timer that will shut the unit down if charge does not terminate in that time. Unit is looking for current to drop to the charger termination current value and end charge. Problem when a system load is added it may be large enough to prevent the charger current from reaching termination current value. After 10 hr the fault is sent and charger shuts down until removed from charger.
    Another approach would be the bq51013B (5V) supplying current to a battery charger with power path.
  • Actually I'm still deciding some aspects, but I can give you some data:

    1) I think battery should be around 1 Ampere / Hour Max, Li-Ion type.

    2) This depends from the battery but I think between 500 mA and 200 mA.

    3) The system is designed around a CC3200Mod with one rgb led and some sensors, I think a max load of 500 mA considering the CC3200 absorbs 250 mA during transmission.

    If I understand it you are suggesting to use  bq51013B that can provide me a 5 Volt 1 Ampere out, and use its out to:

    • supply the CC3200 and the rest of the circuits, using a LDO 3.3v regulator.
    • supply a specific battery charge IC to recharge the battery.

    This could be a good solution, but to switch between the  LDO out and the battery is there any specific device or I've to use a classic solution like double diodes to merge the two power soruces ?

    Using diodes I'll loose at least 0.7 V, could I use schottky diodes?

    Thanks!

    Riccardo