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EVAL Board BQ25504 limited to 110mA ?

Johan Deben
Intellectual 655 points
Other Parts Discussed in Thread: BQ25504, TPS61200

When working with the BQ25504 eval board and after having changed parameters of the BQ25504 to satisfy the application (charging Li battery), we remark that the input current of the card is always fixed at 110mA.

We do not really understand why this is happening.

Is there any way to get more energy out of it, knowing that solar panels are capable of delivering more than 300mA

  • 0
    TI__Guru**** 166176 points

    The bq25504 power switch, and therefore inductor, current is limited to 200mA typical peak (300mA max).  The average input current for most of the Vi/Vo ratios is therefore around 100mA.  You can use two or three bq25504's in parallel, tying their outpus together or move to a larger IC like TPS61200 to access all of the power from your solar panels. 

  • 0 in reply to Jeff F
    Prodigy 145 points

    Hi,

    Is there a limitation on the number of evaluation board's you can place  in parallel?

  • 0 in reply to Adri E
    TI__Guru**** 166176 points

    If you are only connecting the VSTOR pins in parallel, then no.

    Connecting the VIN_DC pins in parallel is not recommended due to each IC trying to actively regulate the voltage at that pin.

  • 0 in reply to Jeff F
    Prodigy 145 points

    Yes we are paralleling only the Vstor.

     

    Thanks!

     

  • 0 in reply to Jeff F
    Prodigy 50 points

    I have a similar need to pull more than 100 mA in certain conditions. I want to size a solar module above the 300 mW limit of the bq25504 in order to increase what can be harvested from low light where typical Vin < 2V with Vbat charge managed between 2.2V to 3.0V (supercap). Less typically, in full sun, the solar module would be capable of 3V @ 500 mA max power point and I'd like to take full advantage. I would prefer not to parallel bq25504 considering space and cost. The bq25504 has too many benefits for me to consider switching to a higher capacity boost or buck-boost.

    Few questions:

    1. Is there a potential for damage to the bq25504 if an energy source is capable of delivering much more current than the 100 mA avg switching limit? Assume I will be careful to clamp the max voltage, just talking about current/power here.

    2. Could I conceivably put a schottky between Vin and Vbat to pass the excess current directly to the supercap when Vin > Vbat + Vdiode or would that interfere with the inductor boosting when Vin < Vbat?

    3. If not a schottky, would you suggest FETs controlled as follows? Q1 switches source+ to Vin. Q2 switches Vin to Vbat. If Vin > Vbat: Q1 = OFF, Q2 = ON. If Vin <= Vbat: Q1 = ON, Q2 = OFF.

    4. Is there another way I can handle the > 100 mA avg with Vin > Vbat scenario on the bq25504?

  • 0 in reply to Erik Dahlgren
    TI__Guru**** 166176 points

    Regarding 1, the bq25504 switch is peak current limited to ~ 200mA which means the average input current at max switching frequency is 100mA.

    Regarding 2, schottky diode bypass is good if source voltage > VSTOR_CHGEN (~1.8V) + 0.3V because you can simply bypass cold start.  If source voltage is less than VSTOR_CHGEN then the IC will enter cold start and you  may not have enough voltage to even turn on the schottky.

    Regarding 3, FET option works all the time, regardless of source voltage level but can be challenging to control the switch over if source is power limited (which does not seem to apply to you)

    Regarding 4, none that I have thought of yet.

    Keep in mind that the IC's MPPT circuit is expecting a high impedance source and will try to regulate the voltage at VIN_DC to the MPP set point.  If you do not need MPPT, you can disable it on the bq25504.