• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 658 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24297: Can I omit the switching parts from my design if OTG is not desired?

samuel williams
Prodigy 40 points
Part Number: BQ24297

I'm having some issues understanding the BQ24297 datasheet/application schematic. I'm not 100% sure but I believe the switching inductor/path is for USB OTG mode, is that correct? If so and I do not require USB OTG can I omit these parts from my design and leave the associated pins floating? Also from what I understand from the datasheet is that the IC will not set a 3A charge current itself, it will only up it to 2A if an external adapter is detected; so I would have to manually set it via I2C to a 3A charge current? 

  • 0
    TI__Expert 8230 points
    Hello Samuel,

    The switching converter on the bq24297 provides the current to the system and the battery when in buck mode (when the VBUS is connected). During OTG mode, if the VBUS is not present, the switching converter is operated in boost mode to boost the battery voltage and provide the OTG output.

    This means the switching node components (inductor, decoupling capacitors at SYS) are needed to complete the switching converter circuit.

    Regarding the charge current, you are correct, the default charge current is 2A, if your application requires 3A charge current, this must be modified via I2C.

    Hope this helps.
  • 0 in reply to Fernando Lopez
    Prodigy 40 points
    Can you clarify what you mean by provides current to the system? I don't see in any application example where this "system" connections go, would I tie that directly to the battery being charged as well?
  • 0 in reply to samuel williams
    TI__Expert 8230 points
    Hello Samuel,

    The bq24297 is a NVDC power-path device; this means that it can provide power to a system load by regulating the input down to a minimum system voltage regulation (MINSYS). Whenever the input is applied and the battery voltage is below MINSYS (by default it's 3.5V, but can be modified via I2C from 3V - 3.7V), the SYS pin will be regulated to MINSYS. If the battery voltage is higher than MINSYS, the SYS pin follows the battery voltage. Essentially, the SYS pin will see a voltage range from MINSYS to VBATREG.

    In an application, any loads (for example, additional power stages, hosts, etc.) will be connected to SYS pin. The battery is always connected to the BAT pin. Page 42 of the bq24297 datasheet has a typical application schematic where it shows the battery connection at BAT pin, and the SYS output.
  • 0 in reply to Fernando Lopez
    Prodigy 40 points

    Okay that helps me out alot, but another question if I may. You said it regulates "down" to a specified voltage. Does this mean the switch mode part of the circuit only operates in buck mode or is it a buck/boost circuit? My battery voltage would vary from 2.5V (full drain) to 4.2V (full charge) and it'd be great if I could use the integrated SYS SMPS to get that 3.5V at any battery voltage range.

  • 0 in reply to samuel williams
    TI__Expert 8230 points
    If the VBUS is present, and OTG is disabled, it operates in buck mode. If VBUS is not present, OTG is enabled and the battery is above VBAT Good threshold, it operates as boost and provides the 5V OTG output at the input.

    If you need a fixed 3.5V output at any battery voltage, you would need a separate power stage connected at SYS that operates from 3.5V to 4.2V (MINSYS to VBAT) and provides 3.5V.