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bq25504 evm charging batteries

Pavlos Lamprou
Prodigy 70 points

I m planning of using this evaluation kit to connect my wsn with a solar panel and a battery storage system.

First thing I would like to ask, is the mote powered by the storage device or via the solar panel too? What I read somewhere in the datasheet is that the device is supposed to have as priority to charge the battery. So I dont get if the mote can consume the power directly supplied from the panel.

The mote consumes under 100mW max (as it is in sleep mode most of the time)  and like most WSN it operates from 2.-3.6V. What do you think I should use for a storage device? (currently the mote is supplied by 2 AAA Alkaline batteries)

  • 0
    Prodigy 70 points

    Can anybody answer? I find it hard to understand how the vstor and vbat voltage is related to the Vin. How can I handle the voltage to be 3V on my device?

  • 0 in reply to Pavlos Lamprou
    TI__Guru**** 166556 points

    VBAT is where the rechargeable battery is connected.

    VSTOR is the output of the boost charger and is typically where the system load is connected.  If VSTOR is below 1.8V, the solar panel at VIN_DC powers a low efficiency cold start circuit to raise the VSTOR voltage to 1.8V.  The system load should be isolated from VSTOR during this time.  Once the VSTOR voltage is above 1.8V, the main boost charger circuitry turns on and draws up to 100mA average from the solar panel and regulates the input voltage to the MPP voltage.  Once VSTOR is above the VBAT_UV threshold, the PFET between VSTOR and VBAT turns on, effectively shorting VSTOR=VBAT.  Please keep in mind that the PFET's body diode always connects VSTOR to VBAT (i.e., VBAT = VSTOR - diode drop).    The boost charger dumps bursts of energy to VSTOR=VBAT until VSTOR=VBAT reaches the VBAT_OV threshold.

    If the battery's maximum charge voltage is 3.0V then VBAT_OV should be set to 3.0V.

  • 0 in reply to Jeff F
    Prodigy 70 points

    "The system load should be isolated from VSTOR during this time". So I dont just connect the load to the STOR pin of the EVM? Does the EVM isolate the load? Or something else should be added? And what do you mean up to 100mA draw from the solar panel? if there is no available power provided by the panel? And how is the Vin connected to Vbat and Vstor? If Vin from the panel is 1V,2V or 3V what will be the Vbat and Vstor?

    One important thing.Does the load draw power from the rechargeable battery when there is no input power from the pv?

     

  • 0 in reply to Pavlos Lamprou
    TI__Guru**** 166556 points

    If you system does not draw power with VSTOR less than 1.8V, then no isolation is necessary.  If it can, then I suggest a PFET in series between the system and VSTOR.  If the PFET's VTH is higher than 1.8V then you can simply tie its gate to ground.  Otherwise, you can use a NFEFT with gate drive by VBAT_OK to drive the gate of the PFET.