Battery protection unit (BPU)

Single-module batteries are typical for applications with voltage range not exceeding 150 V, such as battery-powered tools, vacuum cleaners, multicopter, robots, e-scooters, e-bikes, low voltage telecom, and server UPSs.
Discover the best-fit products for your design for single-module batteries.

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.
Discover the best-fit products for your design for multi-module batteries.

In the high side protection, the disconnect MOSFETs are connected in series with the positive terminal of the battery pack.

Benefits: No bypass of the ground, no hanging ground.

Drawback: Requires gate drivers with charge pumps to drive the MOSFETs.

In the low side protection, the disconnect MOSFETs are connected in series with negative terminal of the battery pack.

Benefits: Easy to implement, requires no charge pumps for the gate drivers.

Drawbacks: Hanging ground → potential of ground bypass via the battery housing and impact on communication & operation.

In common source configuration, the 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. Such a configuration of the MOSFETs can also be referred to as a back-to-back configuration.

Benefits: 

• Can switch faster.
• Less expensive.
• Need only one charge pump or isolated supply is required. 
• Need only one gate driver to drive the two MOSFETs.
• Less complex design.

Downsides:

• Less thermal Dissipation area for MOSFETs with standard Drain down packages. Since the heat generated by MOSFETs dissipates into the copper, which is connected with the control and sensing circuits. Thus affecting the accuracy and efficiency of the control and sensing solution.
• In case of a failure, while using a single gate driver, both MOSFETs will likely fail simultaneously.

In common drain configuration, the 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. Such a configuration of the MOSFETs can also be referred to as a back-to-back configuration.

Benefits:

• Possible to control the FETs independently. 
• Easy to implement safe commutation techniques. 
• Higher safety standard, due to need separate gate drivers to drive the MOSFETs.

Drawbacks:

• Need a charge pump to drive both MOSFETs.
• More complex design.

In this type of topology, the battery charger and the load ports are separated. Such a topology is commonly used, when:

1. the charging currents and discharging currents are different (charging currents are usually much lower than discharging currents).
2. the battery is separated from the load when charged.

Benefits: 

• Lower thermals due to lower path resistance.
• Requires fewer MOSFETs.

Drawbacks:

• Easy to bypass the reverse polarity protection.
• Source to source topology could only be used on the high side, whereas drain to drain could be used on the low side.

High Side	Low Side

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 is 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

With P-MOSFET	Precharge with N-MOSFET

During short circuit conditions, the MOSFETs must not only withstand the rise in the current but also 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 and 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 OptiMOS and StrongIRFET technology offer wide Safe Operating Areas (SOA) and rugged linear mode devices to enable safe and reliable eFuse functionality.  Additionally, Infineon devices have low ΔV_GS,Th, which enables devices to share equal current between parallel MOSFETs during switch on & switch off transients.

• Get an overview of the main feature set of this 48-volt capable EiceDRIVER™.
• Understand its different integrated protection mechanisms.

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•  Get an overview of the main features of this flexible EiceDRIVER™ device
•  Understand its different integrated protection mechanisms

Watch now