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BQ25703A: Only using as a buck charger，can I use only 2 mos？

user6364061
Prodigy 40 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQ25731

Hi

    As a buck-boost charger, we should use 4 mos. 2That id 2 mos before L as buck charger function(Q1/Q2)， and 2 Mos after L as boost charger(Q3/Q4）.Q1/Q3 highside，Q2/Q4 low side.

   My application only use bq25703A as buck mode charger with input voltage 18-20V and 3s Lion battery which highest volatge is 13.2V. Can I only use 2 buck-mode mos before L. So it cost fewer space，and I can use larger mos footprint to improve the heat performance. Meanwhile I still use the NVDC architecture to supply the system.

Thanks

  • 0
    Prodigy 40 points

    The same question also applies to bq25731.

  • 0 in reply to user6364061
    TI__Genius 11385 points

    Hi,

    No, unfortunately you cannot remove the 2 MOSFETs for buck only application. You need to have all 4 switches in both ICs.

    Thanks and I hope this helps,

    Peng

    *If my answer solves your question, please press "This Resolved My Issue" on the thread.  

  • 0 in reply to Pengzhao Zhu
    Prodigy 40 points

    I want to know the reason. As I know, buck only use 2 mos is ok. 

    If there must be 4 mos, the can they have different requirment?  eg. Q1/Q2 have both low rds and low Qg. Q3 only low rds as it always on, and Q4 has no requirements as it's always off. So I can choose different mos

  • 0 in reply to user6364061
    TI__Genius 11385 points

    Hi,

    The charger uses the FETs for other functions. For example, the boost high side blocks the current in case of input short. Due to the inherent body diode of the buck high side, the battery can discharge if the input is shorted. As opposed to other DC-DC converters where only some caps are available at the output, the presence of a high energy battery will require some mechanism to prevent accidentally discharge. Please have all 4 MOSFETs if you use the BQ25703A.

    The other option is to explore some of our buck chargers for your application:

    https://www.ti.com/power-management/battery-management/charger-ics/products.html 

    Yes, you can select different MOSFETS tailored to your application.

    Thanks and I hope this helps,

    Peng

    *If my answer solves your question, please press "This Resolved My Issue" on the thread.  

  • 0 in reply to Pengzhao Zhu
    Prodigy 40 points

    Do you have some recommend solution which requirments are as below

    1. VIN 20V; 3s battery;5A charge current

    2. Support NVDC, and bat mos is PMOS

    3. support I2C can monitor battery voltage and current.

    Thanks

  • 0 in reply to user6364061
    TI__Genius 11385 points

    Hi,

    I would recommend you to take a look at our integrated buck-boost BQ2579x parts. It is lower powered but it seems to be enough for your application. The integrated MOSFETs will allow you to save some cost as well as having a smaller form factor. For higher power and flexibility of the power stage (to choose any MOSFETs), the buck-boost controllers (which include BQ25703A) would be suitable.

    Thanks and I hope this helps,

    Peng

    *If my answer solves your question, please press "This Resolved My Issue" on the thread.