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BQ24295: Device recommendation for BMS circuit design

Linda Igboanugo
Intellectual 1820 points
Part Number: BQ24295
Other Parts Discussed in Thread: LP2985, , BQ25606, BQ25100, BQ24075, BQ25120A

Hello, 

Can you give a recommendation for a BMS that would meet the below spec's?

Application is for a 24hr battery back up system in building automation product

- using a single cell Li-ion battery with a discharge current of 100mA (estimate!).

- need to be able to recharge the battery in 24hrs, so quite low currents actually.

- original design uses an external 5V PSU and the on-board CPU of design requires a 3.3V supply.

original plan is the LP2985 (another TI device) 3V3 LDO regulator which we already have coded.

 - We do not require any of the USB protocol on the BQ24295

 - An  IC is good for us, since it was a complete power controller, handling the charging of Li-ion with the automatic switch over the battery back-up. So, a stand-alone power controller would be ideal. but cost target is near $0.4

- We can handle some software configuration but totally stand-alone would be even more popular!

Will appreciate the input. 

Regards

Linda

  • 0
    TI__Mastermind 25800 points
    Hey Linda,

    I would check out the BQ25606 as a standalone option. It does have the USB detection, but these pins can be left open and solely rely on the ILIM pin to limit the input current limit.

    You will still likely need the LDO as these chargers allow the integrated converter track the system voltage with the battery voltage down to a minimum voltage.

    If you need something more simple, we do have some linear chargers as well that can be programmed with resistors and capacitors.

    My only question is the stipulation about 24 charge time: Can the device charge faster or will the charge current be so low that the expected charge time is potentially 24hr?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    TI__Intellectual 1820 points

    Hi Joel,

    I have some further feedback on this: can you help? Do you cover the BQ25100? c

    In essense we want to understand  suitability of the BQ25100 and BQ24075 if you can comment on suitability for the application. and pointers to help get a design going..

    1) BQ25100 – I am a little puzzled by the constant connection to the battery.

    I thought Li-Ion should be disconnected from the charging source when fully charged?

     

      -- I can send in email

     

     

    2) BQ25606 & BQ25120A both look OK, BUT, BQ24075 also looks OK and has the massive advantage of being coded on existing systems.

    Any comments regarding this device?

     

    Just to reiterate requirement:

     

    1) 5V external PSU (although it could be 9V or 12V if required)

    2) Single cell Li-Ion back-up battery with 100mA load with a maximum 24 hour recharge time.

     

    Please note also: I can send in email more details on the 24hr charge requirement if needed.

     

    Can you advice ?

     

    Kind Regards

    Linda

  • 0 in reply to Linda Igboanugo
    TI__Mastermind 25800 points
    Hey Linda,

    For 1) The input is disconnected from the battery once battery charging has terminated. You can see this achieved by the back-to-back FETs from the input to the output. However, termination is current based and because the system and battery share the IOUT current, any load current pulled by the system has the potential to prevent termination. In other words, system current is not differentiated from battery charging current.

    For 2) This charger is a linear charger with integrated power path, meaning the battery and system voltage rails are isolated from one another. In this system, charging can terminate separately while the input still provides power to the system. There is also instantaneous backup if the input is overloaded/removed/etc.

    If the 24-hr charge time requirement is based on a large battery with a small charging current, the BQ24075 has a safety timer that can be programmed or disabled while the BQ25100 does not. If you need to charge it faster, then the 24hr charge time is a non-factor as this will be based on the power capability of your input and the capacity of the battery. For higher voltages, you will see higher loss through a linear charger so consider the BQ25606 to improve charging efficiency for the higher voltages.


    Regards,
    Joel H