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BQ24450: Technical Support Request for Developing Lead-Acid Battery Charger

Mohd Sahid
Prodigy 80 points
Part Number: BQ24450
Other Parts Discussed in Thread: BQ25750, BQ25756, BQ24650

Tool/software:

Dear Texas Instruments Support Team,

I am currently engaged in developing a lead-acid battery charger for a specific application. We are considering Texas Instruments solutions for this project and seek your expert guidance to ensure optimal performance and reliability.

Project Specifications

  • Battery Type: Lead-Acid
  • Input Voltage: 40-60V DC
  • Charging Voltage: 54V (Boost Voltage)
  • Float Voltage: 53V
  • Constant Charging Current: 10A

We are looking for recommendations on the appropriate Texas Instruments components that would be suitable for this application. Specifically, we need support in the following areas-

  1. Component Selection:
      • Suggestions for DC-DC converter controllers that can handle the specified voltage and current requirements.
      • Information on any evaluation modules or reference designs available for high-power lead-acid battery charging.

    2. Configuration and Setup:

      • Detailed guidelines on configuring the selected components to achieve the desired boost voltage of 54V and float voltage of 53V.
      • Recommendations for any additional circuitry or components required for precise voltage and current regulation.

    3. Protection Mechanisms:

      • Guidance on implementing protection features such as over-voltage, over-current, and short-circuit protection.

    4. Optimization for Lead-Acid Battery Charging:

      • Specific considerations or optimizations for using Texas Instruments solutions in lead-acid battery charging applications.
      • Tips on achieving a smooth transition between the boost voltage and float voltage.
  • 0
    TI__Guru** 105760 points

    Hello Mohd,

    Sorry for the delay, we will respond by the end of day tomorrow CST.

    Sincerely,

    Wyatt Keller

  • +1 in reply to Wyatt Keller
    TI__Mastermind 31085 points

    Hello Mohd,

    We have a lead acid battery charger variant of the BQ25750. This should come out 4Q. Does this work for your timeline?

    This IC is pin-to-pin with BQ25750 and has a direct power path. You can use the BQ25750 to develop your application.

    Let me know if this works for you and we will try to get more information about this application by early next week.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 80 points

    Dear Ethan,

    Thank you for your prompt response and for providing initial guidance. The information regarding the upcoming lead-acid battery charger variant of the BQ25750 is quite helpful, and it seems promising for our timeline and project needs.

    To proceed further, could you please provide more detailed information and support in the following areas:

    1. Component Selection:
    - Could you confirm if the BQ25750 (or its upcoming variant) is suitable for our input voltage range of 40-60V DC and our charging requirements (54V boost voltage, 53V float voltage, and 10A constant charging current)?
    - Are there other components or controllers that you recommend for this application, particularly for high-power lead-acid battery charging?

    2. Configuration and Setup:
    - We need detailed guidelines on configuring the BQ25750 (or its variant) to achieve the desired boost and float voltages. Any application notes or reference designs would be greatly appreciated.
    - Recommendations on any additional circuitry or components required for precise voltage and current regulation would be valuable.

    3. Protection Mechanisms:
    - Could you provide guidance on implementing protection features such as over-voltage, over-current, and short-circuit protection with the BQ25750 or its variant?
    - Any specific considerations for ensuring the safety and reliability of the charging system would be helpful.

    4. Optimization for Lead-Acid Battery Charging:
    - Are there any specific considerations or optimizations for using Texas Instruments solutions in lead-acid battery charging applications?
    - Tips on achieving a smooth transition between the boost voltage and float voltage would be beneficial.

    We appreciate your support and look forward to your detailed guidance to ensure the success of our lead-acid battery charger development.

    Best Regards,
    Mohd Sahid

  • +1 in reply to Mohd Sahid
    TI__Mastermind 31085 points

    Hello Mohd,

    1. Yes, the BQ25750 can work with a 30-60V DC input and charge a 54V battery at 10A. The lead-acid variant should have the same input and output specs. I am unaware of any other part that meets the needs for you application. 

    2. To achieve the desired charge voltage, you will need to change the VFB resistor divider. You can refer the BQ25756 design calculator for how you can adjust this.

    3. The charger already implements over voltage, over current, and short circuit protection. Over voltage protection is controlled by the ACOV/ACUV voltage divider. The design calculator also has tools to help set this. Over current protection is enabled by default and will activate once the voltage across the current sense resistor is too high.

    4. The lead acid variant of the BQ25750 should automatically and cleanly transition between the constant current, absorb and float stages.

    We have some other material which may help. We have a schematic checklist for the BQ25750: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1322803/faq-bq25750-schematic-and-layout-checklist

    Here's the link to the design calculator. This tool should work for any part in the BQ2575X family or BQ2585X family: www.ti.com/.../

    Let me know if you have any other questions about this part.

    Also, will you be using the power path of the charger and will you have a system load? If so, how much will the system load be?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 80 points

    Hello Ethan,

    Thank you for the detailed response and the confirmation that the BQ25750 can meet our requirements. Your guidance on adjusting the VFB resistor divider and the use of the design calculator is very helpful.

    To ensure we fully understand the implementation and achieve the best performance, we have a few additional questions:

    1. PCB and Schematic Design Files

    Could you provide design file of e2e.ti.com/.../faq-bq25750-schematic-and-layout-checklist

    2. Implementing Constant Current Condition

    We would appreciate more details on how to implement the constant current charging condition. Specifically:

    • Configuration Steps: Step-by-step instructions or examples on setting up the charger to maintain the constant current during the bulk charge phase.
    • Monitoring and Adjustment: How to monitor and adjust the charging current if necessary during operation.

    Thank you for providing the schematic checklist and the design calculator link. These tools will be very useful. If there are any other documents, application notes, or example projects with design files related to the BQ2575x series that you think might help us, please share those as well.

    We look forward to your guidance and support to ensure the successful design and implementation of our lead-acid battery charger.

    Best Regards,

    Mohd Sahid

  • +1 in reply to Mohd Sahid
    TI__Mastermind 31085 points

    Hello Mohd,

    1. Yes, we can provide those schematic and board design files:BQ25750_Design_Files.zip

    2. There are two ways to adjust the constant current value. You can change the ICHG pin resistor or you can change the ICHG register. The IC will pick the lower of the two values. This will adjust the charge current to the right values.

    For monitoring and adjustment, I would recommend using a battery monitor to monitor and protect the battery. You can use an MCU to provide to adjust the charge register, turn-off charging, enable HiZ mode, or make slight adjustments to the charge voltage. Let me know if you want me to loop in the battery monitor team to recommend a battery monitor.

    Also, the IC has a pin to read the temperature for a thermistor. The IC will automatically adjust the charge voltage and charge current to account for changes in temperature.

    Let me know if you have any more questions

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 80 points

    Hello Ethan,

    Thank you for providing the information and the design files for the BQ25750. This will significantly aid our development process. I have a few more questions and requests based on your response:

    1. Constant Current Adjustment

    Thank you for explaining the two methods to adjust the constant current value. We have a few follow-up questions:

    • ICHG Pin Resistor: Could you provide guidance or an example calculation on selecting the appropriate resistor value for the ICHG pin to set the charging current to 10A?
    • ICHG Register Configuration: Instructions or examples on how to configure the ICHG register via software to achieve the desired charging current, we are using PIC18F26K80 microcontroller.

    2. Reverse Polarity Protection

    We would like to implement a reverse polarity protection circuit to safeguard the battery and the charger. Could you provide:

    • Circuit Design: A recommended circuit design or example for implementing reverse polarity protection.
    • Component Selection: Recommendations on components (e.g., MOSFETs, diodes) suitable for reverse polarity protection.

    3. System Load Integration

    Regarding the system load:

    • Load Sharing Configuration: Any specific considerations or configurations needed to manage the load sharing between the battery charging and the system load effectively.

    4. Battery Monitoring

    We would like to integrate a battery monitor to oversee and protect the battery. Could you please loop in the battery monitor team to recommend a suitable battery monitor for our application? Specifically, we need:

    • Recommended Battery Monitor: A suitable part number and features that align with our requirements.
    • Integration Guidance: Information on how to integrate the battery monitor with the BQ25750 and our MCU.
    • State of Charge (SoC) and State of Health (SoH): Recommendations for monitoring SoC and SoH of the lead acid battery, and any tools or ICs that can facilitate this.

    Thank you once again for your assistance. We look forward to your guidance and support to ensure the successful design and implementation of our lead-acid battery charger.

    Best Regards,

    Mohd Sahid

  • 0 in reply to Ethan Galloway
    Prodigy 71 points

    Hi Ethan,

    Will this lead acid variant of the BQ25750 be able to handle Li-Ion/LiFePo4 too? I'm wanting to design a battery charger that can handle all three of these chemistries. I have looked at the BQ24650 which in terms of charging looks to fit the bill, but it's pity it doesn't have a lot of the features that the BQ25750 has such as the power path control, reverse mode buck/boost, etc.

    Regards
    Jock

  • 0 in reply to Jock Duncan
    TI__Mastermind 20570 points

    Hi Jock,

    This new variant is going to be for Lead Acid only. However, you can use BQ25750 with the same concept described in the application note in the link below to charge Lead Acid battery.

    https://www.ti.com/lit/pdf/slua992 

  • 0 in reply to Jing Zou
    Prodigy 71 points

    Thanks Jing, that's helpful to know. I have seen that application note before and was hoping the same would apply for the BQ25750. I have also seen another application note for the BQ24650 for adding temperature compensation for charge voltage for lead acid batteries - to prolong the health of the battery at different temperatures. Do you think if I added this feature also, that would make it fairly close in functionality to the lead acid only variant? or are there additional features that would make the new variant still better for lead acid batteries over the BQ25750 with the above mentioned external modifications?

  • 0 in reply to Jock Duncan
    TI__Mastermind 20570 points

    Hi Jock,

    The difference of the new variant is that all these specific charging profile for Lead Acid battery is integrated and can be configured through I2C. The BQ25750 with the workaround concept in the application note should be able to achieve the same function. 

  • 0 in reply to Jing Zou
    Prodigy 71 points

    Great, thanks for the info Jing.