Current Limiting Circuit for 16S LFP Battery Pack – IC Recommendation

DC-DC Power Converters
1

Hello MPS Team,

We are currently working on adding a current-limiting circuit to our 16S LFP battery pack and would appreciate the community’s technical guidance in selecting a suitable TI solution.

Application Requirements

  • Battery Configuration: 16S LFP

  • Maximum Charging Current: 100 A

  • Current-Limiting Condition: When the pack voltage reaches 54 V, the charging current should be limited to approximately 10 A.

  • Control: Standalone solution with MCU-based ON/OFF control

  • Adjustable Current-Limit Range: 3–20 A, allowing the same design to be used for different current-limit requirements

  • Input Voltage Range: 20–120 V

  • Maximum Target Current: 30 A

    • Our initial design target is around 10 A, but we would like the architecture to support higher current levels in future revisions.

  • Package Requirement: Non-BGA package preferred

  • Target BOM Cost: < $10 at a production volume of approximately 1,000–5,000 units

Devices Currently Under Evaluation

Based on our initial evaluation, we have identified the following devices as potential options:

  • MP9931

  • MP2908A

However, we are open to considering other MPS devices or alternative architectures that may be better suited to our requirements.

We would particularly appreciate guidance on:

  1. The most suitable MPS IC/architecture for implementing this current-limiting function.

  2. Whether the above devices can meet the 20–120 V input range and 3–20 A adjustable current-limit requirement.

  3. A recommended power-stage topology for achieving the required current limiting with good efficiency and thermal performance.

  4. Recommended methods for implementing MCU-based ON/OFF control.

  5. Any relevant TI reference designs, evaluation modules, application notes, or existing reference circuits that we can use as a starting point.

  6. Recommendations for achieving the target BOM cost while maintaining adequate reliability for a battery application.

Our goal is to develop a compact, cost-effective, and scalable solution that can initially support approximately 10 A and potentially scale to 30 A in future versions.

We would greatly appreciate any recommendations or feedback from the MPS community that could help us select the right device and architecture.

Thank you in advance for your support.

Regards,
Santu R

2

Hi Santu,

Thank you for sharing your requirements. If your existing charger supports an adjustable current setpoint, reducing it at 54 V could help minimize additional cost and power loss. For a separate regulating stage, a synchronous buck architecture could work if the input stays sufficiently above the pack voltage; operation both below and above the pack voltage would require buck-boost conversion.

The MP9931 and MP2908A you identified both follow the synchronous buck architecture with external MOSFETs, so your selections align with that approach.

To help us find you some more solutions in our portfolio,

  • Is 120 V continuous or a transient, and must charging operate across the full 20–120 V range?

  • Must the added circuit carry 100 A below 54 V, or is there a separate charging path?

  • Does the existing charger support an adjustable current setpoint?

  • Should the 54 V transition happen automatically in hardware, with the MCU used only for ON/OFF?

  • Does the <$10 BOM target include the complete power stage?

-Hannah

3

Hi Hannah,

I would like to add a few more details to clarify our current-limiting circuit requirement.

We are looking for a current-limiting circuit that is activated when the battery pack reaches approximately 90% SOC. At this point, we want to reduce the charging current from 0.5C to approximately 0.1C.

Our current battery pack configuration is:

  • Battery chemistry: LFP

  • Configuration: 16S

  • Capacity: 100 Ah

  • Normal charging current: 0.5C = 50 A

  • Reduced charging current: 0.1C = 10 A

  • Pack voltage: 54 V trigger point at approximately 90% SOC

  • Maximum charging voltage: approximately 58 V

  • Charger voltage capability: up to 60 V

  • BMS: Existing BMS capable of handling up to 100 A continuous charging current

The intended operation is as follows:

  1. During normal charging, the BMS allows the battery to charge at the normal charging current.

  2. When the pack reaches approximately 90% SOC / Vpack = 54 V, the MCU detects this condition.

  3. The MCU then turns ON the current-limiting circuit.

  4. At the same time, the MCU turns OFF the BMS MOSFETs, transferring the charging path to the current-limiting circuit.

  5. The current-limiting circuit then limits the charging current to approximately 10 A (0.1C) until the battery reaches the required final charging condition.

The charger itself does not support an adjustable current setpoint, so the current reduction needs to be implemented externally through the current-limiting circuit.

Also, to clarify the cost requirement mentioned earlier, the target cost applies only to the current-limiting circuit and does not include the existing BMS.

I hope these additional details clarify the intended operating conditions and system architecture.

Please let me know if you have any recommendations regarding the suitable topology or IC/device for implementing this current-limiting function.

Looking forward to your suggestions.

Thank you,
Santu