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Original question:

BQ33100: Reference design for bq33100 with bq24640

BQ33100: Reference design for bq33100 with bq24640

Chris Jones25
Prodigy 220 points
Part Number: BQ33100
Other Parts Discussed in Thread: BQ24640,

I have a question about the posted schematic for 5 series supercaps. How many amps are they being charged with in this design? 

  • 0
    TI__Genius 10830 points
    hi Chris,
    I do not know what current the schematic was designed for. The design can be modified to whatever current you desire within the threshold that the charger can supply. You will just have to make adjustments to the inductor and switching fets.

    regards,
    David
  • 0 in reply to David Hien
    Prodigy 220 points

    Do you know of any reference designs for 20A charging? If charging with the BQ24640 at 20A does that mean that only 20A can be pulled off the supercaps or can the full current of the supercaps be accessed? 

  • 0 in reply to Chris Jones25
    TI__Mastermind 20300 points
    Hello Chris,

    Unfortunately, we do not have any 20A reference design with bq24640. The bq24640 can support 20A charge current, and does not have control over discharge current of the supercapacitor.
  • 0 in reply to Jing Zou
    Prodigy 220 points

    I'm a bit confused because supercaps don't have separate charging pins and discharge pins. How do you recommend charging them with the BQ24640 while keeping that separate from the discharge circuit? In my application I'm trying to use the supercaps to boost the available current provided by the same power supply that's charging the caps. 

  • 0 in reply to Chris Jones25
    TI__Mastermind 20300 points
    The super cap is charged and discharged through the same terminals. The charger provides charge current to the supercap. If you are discharging the supercap, where are you discharging it to? The charger does not control this discharging path. You can discharge your supercap at any rate that your supercap spec is rated for if you directly connect the load at the supercap. The charger does not have control over this discharging path.
  • 0 in reply to Jing Zou
    Prodigy 220 points

    My discharge net and charging net are the same. Here's a basic block diagram of the current scenario. I'm trying to get rid of the external relay and do everything on the board. I'm trying to use the supercaps to boost current capacity of the power supply at motor startup (milliseconds). 

  • 0 in reply to Chris Jones25
    TI__Mastermind 20300 points
    I do not see bq24640 in your block diagram... Please refer to the bq24640 for the charger operation.
  • 0 in reply to Jing Zou
    Prodigy 220 points
    That's my current solution. I'm trying to get some help with how I can use the bq24640 and bq33100.
  • 0 in reply to Chris Jones25
    Prodigy 220 points

    Can the BQ33100 be used without an SMBus programmer? 

    Is there a way to talk to an application engineer on the phone? I have multiple unanswered questions on here. 

    Thanks. 

  • 0 in reply to Chris Jones25
    Prodigy 220 points
    The original schematic was supposed to be 10A. But upon reviewing the datasheet and the resistor values it looks like 1A.

    I[charge] = V[iset] / 20 * R[sr]
    V[iset] is a 3.3V reference run through a voltage divider of (100k and 6.49k) which lowers the voltage down to 0.2V.
    R[sr] is 0.010 ohms
    0.2V / 20 * 0.010 ohm = 1 A.

    So if I change R2 in the voltage divider to about 150k voltage would change to 1.98V
    and R[sr] to 5 mOhm

    1.98V / 20 * 0.005 = 19.8A

    Can someone double check my numbers? Am I thinking about this correctly?
  • 0 in reply to Chris Jones25
    Prodigy 220 points

    Is there a different forum I should be posting in or some other avenue for support I should be taking? 

  • 0 in reply to Chris Jones25
    Prodigy 220 points
    Is there some other forum I should be posting on or a phone number I should call for questions?
  • 0 in reply to Chris Jones25
    TI__Mastermind 20300 points
    Your calculation is correct.
    The current, however, will be affected by the thermal performance of the external components such as the switching FETs.
    Please post BQ24640 related questions in a separate thread to avoid confusion. bq24640 and bq33100 are supported by different group. Thanks.