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BQ40Z50: Compatible charger IC for BQ40Z50 (BQ40Z60 redesign)

Part Number: BQ40Z50
Other Parts Discussed in Thread: BQ40Z60, BQ24800, BQ25720, BQ24610, BQ24800EVM

Hello fellow engineers,

We're currently working on a redesign of a product which contains a BQ40Z60. The charge controller will be replaced by the BQ40Z50 and an SMBUS controlled charge IC. The application has a charge voltage of 24VDC +/- 5%. The battery is a 4 cell lithium pack. The charger voltage will never drop below the maximum battery voltage, so a buck controller would be fine.

The preferred option will be the BQ24800, but the datasheet lists a recommended maximum input voltage of 24V with an absolute max of 30V. Can this IC safely be used with the previously mentioned charge input voltage?

Another option will be the BQ25720, but this is a buck-boost converter, meaning that it contains two more MOSFET than a buck converter. Those MOSFETs will never be utilized since the input voltage is always higher than the battery voltage.

Is there any charge IC that can replace the BQ40Z60s built in charger without needing two extra MOSFETs and works up to 26V like the BQ40Z60?

Kind regards,

Svenn

  • Hello Svenn,

    I think your questions are more related to the chargers you linked than the BQ40Z50 gauge, I have assigned this thread to the charger team.

    Sincerely,

    Wyatt Keller

  • Hi Svenn,

    Please take a look at BQ24610: Standalone 1-6 cell Buck battery charge controller with 5V-28V input

    https://www.ti.com/product/BQ24610

    If SMBus is required, BQ24800 is the choice, but it could not operation at input voltage higher than 24V. 

    Regards,

    Tiger

  • Hi Tiger,

    The BQ24800 looks useful, but I can't get acces to a datasheet.

    I already filled in the request form three days ago, but didn't get any response. Can you please send the complete documentation?

    This design seems to use a lot of extra components compared to the BQ40Z60 design. Is it possible to omit the Rac shunt resistor and BATFET MOSFET?

    Kind regards,

    Svenn

  • Hi Svenn,

    Not suggest to omit the RAC shunt resistor and BATFET MOSFET. To get started with BQ24800, please order a BQ24800EVM online. 

    Regards,

    Tiger

  • Hi Tiger,

    I'd like to receive the full BQ248000 documentation to make sure it's suitable for our application before ordering the EVM.
    Can you please send this?

    What is the reason to not remove the shunt resistor and BATFET MOSFET? I added a picture to explain the way we intend to connect the BQ40Z50 and BQ24800.

    When using the BATFET to discharge the battery, the full current (in our case 12A max) needs to go though the charger shunt resistor (R9) when following the EVM schematics. When using the recommended shunt resistor of 10mOhm, the power loss will be too large (1,7W). So can we remove the BATFET and connect the pack directly to our load just like the BQ40Z60 design?

    We chose the BQ40Z50 because it can operate with a lower value shunt resistors then the BQ40Z60 which we are currently using to have a more efficiënt system which can operate with less heat production. 'Upgrading' to this new design will result in even more power loss in shunt resistors following the EVM schematics.

    This new design will also add the shunt resistor (R3) which will result in extra power dissipation when charging. Since the charge current to the battery is measured through R9, what does this resistor do and can we remove it?

    So is it possible to remove the BATFET as shown in the picture and remove shunt R3? Can you please give us a more comprehensive answer to all of my questions?

    Regards,
    Svenn





  • Hi Svenn,

    Let me check with the person who approve your datasheet request next week, who is in travel now. 

    To answer your questions, it is best to review your design. Thanks for providing the schematic. If you don't need the power path feature, you can remove the BATFET. 

    If you remove the R3 shunt resistor, the charger will not detect the input current information, thus lose the adapter overload protection (ACOC) or input current dynamic power management capability (IINDPM). IINDPM maximizes the input power capability. 

    Is that a risk you want to take? Even though the BQ40Z50 has additional protection feature, but this information is not available to the charger.

    Hope this helps.

    Regards,

    Tiger

  • Hi Tiger,
    Thank you for your response. We are looking forward receiving the datasheet so we can read about the ACOC and IINDPM features.
    Kind regards,
    Svenn