Battery protection units (BPU)

Solutions that enable easy design-in and ensure safe charging and discharging, preventing battery damage and failure

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Overview

The high power density of lithium-ion batteries has made them very popular. However, the unstable behavior of lithium-ion cells under critical conditions requires them to be handled with care. This means a battery management system (BMS) is needed to monitor battery state and ensure the safety of operation. Part of that BMS is the battery protection unit (BPU), which prevents possible damage to the battery cells and the failure of the battery.

Benefits

  • High performance with lower RDS(on)
  • Wide safe operating area (SOA)
  • Low-cost solution
  • Low component count
  • Effective parallelization solutions
  • Short-circuit protection
  • High current rating capability
  • Tailored turn-on and turn-off times
  • MOSFET protection up to 600 V
  • Single- and multi-module available

Block diagram

About

Battery protection unit (BPU) in BMS

A battery protection unit (BPU) prevents possible damage to the battery cells and the failure of the battery, enhancing the useful operating life of lithium-ion batteries by protecting the battery pack against charge current, discharge current, and pack short fault conditions.

Infineon's battery protection solutions offer many key benefits, including higher performance with lower RDS(on), wider safe operating area (SOA), lower cost solutions with a more compact bill of materials and more effective parallelization solutions, short-circuit protection with higher peak current rates, turn-on and turn-off solutions tailored to application needs, and up to 600 V MOSFET protection solutions (including single- and multi-module). 

Check out the block diagram and the other content on this page for more details.

Failure to disconnect

Failing to disconnect the battery during dangerous conditions can lead to the following problems:

  • Thermal runaway often due to overcharging or overheating of the battery. The overheating event can be due to a rise in the ambient temperature or due to charging/discharging the batteries with high current rates. Thermal runaway damages the battery cells and can lead to fires
  • Death of the cell often due to the discharge of batteries below their specified thresholds
  • Damage to the load device often due to either improper inrush current management or reverse polarity

In order to prevent these failures, Infineon offers a wide range of battery protection solutions that increase the lifetime and efficiency of lithium-ion batteries under stressful conditions.

Battery pack architectures

There are two types of battery architecture in use today:

  • Single-module batteries are typical for applications with a voltage range not exceeding 150 V, such as battery-powered tools, vacuum cleaners, multicopters, robots, e-scooters, e-bikes, low-voltage telecom, and server UPSs.
  • Multi-module batteries are typical for applications with high-voltage batteries, including automotive, e-forklifts, e-boats, residential and utility size energy storage systems, and UPSs.

Infineon offers BPU solutions for both architecture types. 

Learn more about single-module batteries
Learn more about multi-module batteries
Protection topologies

When it comes to protection topologies, many are in use:

  • High-side protection: Disconnect MOSFETs are connected in series with the positive terminal of the battery pack. 
  • Low-side protection: Disconnect MOSFETs are connected in series with negative terminal of the battery pack.
  • Source-to-source protection circuit: MOSFETs are connected in series with their sources connected to each other and drain terminals of the MOSFETs forms in and out of the protection circuit. 
  • Drain-to-drain protection circuit: MOSFETs are connected in series with their drains connected to each other and source terminals of the MOSFETs forms in and out of the protection circuit. 
  • Separate charge and discharge ports: The battery charger and the load ports are separated. Commonly used when the charging currents and discharging currents are different (charging currents are usually much lower than discharging currents) and the battery is separated from the load when charged.
BPU short-circuit protection

During short-circuit conditions, the MOSFETs must not only withstand the rise in current but also the possibility of avalanching during turn-off. The MOSFETs and circuitry which detect faults and disconnects the battery or load are referred to as eFuse. Avalanching of an eFuse might occur since during a short-circuit, the MOSFET needs to be turned off fast. This in turn will result in short high-current pulses that flow into the inductance, which is created by the wires connecting the battery pack with the load - and by the load itself. The parasitic inductance can induce enough voltage to result in the avalanching of the MOSFETs which will turn the loads' inductance into a voltage generator, ramping up the voltage across the protection solution beyond the maximum allowed voltage.

Infineon's OptiMOS™ and StrongIRFET™ MOSFET technologies offer wide safe operating areas (SOA) and rugged linear mode devices to enable safe and reliable eFuse functionality. Additionally, Infineon devices have low ΔVGSTh, which enables devices to share equal current between parallel MOSFETs during switch on and switch off transients.

BPU load inrush current protection

Inrush currents arise during turn-on, mainly when the battery is first connected to the load. The inrush currents can get high enough to either blow off the protection fuse or lead to switching off of the protection MOSFETs due to false indications of overcurrent or short-circuit alarm. An inrush current limiting circuit limits the inrush current during the turn-on phase and protects both the battery and the load. 

  • The pre-charge circuit is required whenever any of the following conditions are true:
  • The load has high input capacitance, which will be damaged by the inrush current
  • The main fuse will blow off if the turn-on current exceeded the fuse's limit
  • The contactors, if present, will be damaged by the inrush current
  • The battery cells are not rated for the inrush current
  • The MOSFETs are not rated for the inrush current
  • The precharge circuit often consists of a MOSFET with high resistance path

Battery protection unit (BPU) in BMS

A battery protection unit (BPU) prevents possible damage to the battery cells and the failure of the battery, enhancing the useful operating life of lithium-ion batteries by protecting the battery pack against charge current, discharge current, and pack short fault conditions.

Infineon's battery protection solutions offer many key benefits, including higher performance with lower RDS(on), wider safe operating area (SOA), lower cost solutions with a more compact bill of materials and more effective parallelization solutions, short-circuit protection with higher peak current rates, turn-on and turn-off solutions tailored to application needs, and up to 600 V MOSFET protection solutions (including single- and multi-module). 

Check out the block diagram and the other content on this page for more details.

Failure to disconnect

Failing to disconnect the battery during dangerous conditions can lead to the following problems:

  • Thermal runaway often due to overcharging or overheating of the battery. The overheating event can be due to a rise in the ambient temperature or due to charging/discharging the batteries with high current rates. Thermal runaway damages the battery cells and can lead to fires
  • Death of the cell often due to the discharge of batteries below their specified thresholds
  • Damage to the load device often due to either improper inrush current management or reverse polarity

In order to prevent these failures, Infineon offers a wide range of battery protection solutions that increase the lifetime and efficiency of lithium-ion batteries under stressful conditions.

Battery pack architectures

There are two types of battery architecture in use today:

  • Single-module batteries are typical for applications with a voltage range not exceeding 150 V, such as battery-powered tools, vacuum cleaners, multicopters, robots, e-scooters, e-bikes, low-voltage telecom, and server UPSs.
  • Multi-module batteries are typical for applications with high-voltage batteries, including automotive, e-forklifts, e-boats, residential and utility size energy storage systems, and UPSs.

Infineon offers BPU solutions for both architecture types. 

Learn more about single-module batteries
Learn more about multi-module batteries

Protection topologies

When it comes to protection topologies, many are in use:

  • High-side protection: Disconnect MOSFETs are connected in series with the positive terminal of the battery pack. 
  • Low-side protection: Disconnect MOSFETs are connected in series with negative terminal of the battery pack.
  • Source-to-source protection circuit: MOSFETs are connected in series with their sources connected to each other and drain terminals of the MOSFETs forms in and out of the protection circuit. 
  • Drain-to-drain protection circuit: MOSFETs are connected in series with their drains connected to each other and source terminals of the MOSFETs forms in and out of the protection circuit. 
  • Separate charge and discharge ports: The battery charger and the load ports are separated. Commonly used when the charging currents and discharging currents are different (charging currents are usually much lower than discharging currents) and the battery is separated from the load when charged.

BPU short-circuit protection

During short-circuit conditions, the MOSFETs must not only withstand the rise in current but also the possibility of avalanching during turn-off. The MOSFETs and circuitry which detect faults and disconnects the battery or load are referred to as eFuse. Avalanching of an eFuse might occur since during a short-circuit, the MOSFET needs to be turned off fast. This in turn will result in short high-current pulses that flow into the inductance, which is created by the wires connecting the battery pack with the load - and by the load itself. The parasitic inductance can induce enough voltage to result in the avalanching of the MOSFETs which will turn the loads' inductance into a voltage generator, ramping up the voltage across the protection solution beyond the maximum allowed voltage.

Infineon's OptiMOS™ and StrongIRFET™ MOSFET technologies offer wide safe operating areas (SOA) and rugged linear mode devices to enable safe and reliable eFuse functionality. Additionally, Infineon devices have low ΔVGSTh, which enables devices to share equal current between parallel MOSFETs during switch on and switch off transients.

BPU load inrush current protection

Inrush currents arise during turn-on, mainly when the battery is first connected to the load. The inrush currents can get high enough to either blow off the protection fuse or lead to switching off of the protection MOSFETs due to false indications of overcurrent or short-circuit alarm. An inrush current limiting circuit limits the inrush current during the turn-on phase and protects both the battery and the load. 

  • The pre-charge circuit is required whenever any of the following conditions are true:
  • The load has high input capacitance, which will be damaged by the inrush current
  • The main fuse will blow off if the turn-on current exceeded the fuse's limit
  • The contactors, if present, will be damaged by the inrush current
  • The battery cells are not rated for the inrush current
  • The MOSFETs are not rated for the inrush current
  • The precharge circuit often consists of a MOSFET with high resistance path

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