The components of BMS are: △Battery Protection Unit that protects the battery by positioning MOSFETs, etc. △Cell Monitoring & Balancing (CMB) that monitors the voltage of each cell and balances the charging △Battery Monitoring & Control Unit that communicates with the outside world △Current Sensor that senses the charge/discharge current of the battery △PMIC or regulator that supplies power to each unit.

The battery protection function protects battery cells from overcharge/discharge, blocks inrush current from the outside, and efficiently manages heat generated during charging and discharging.

CMB monitors cell voltage, temperature during charge and discharge, and overall voltage of battery packs connected in series.

BMS configuration varies depending on the application.

Applications such as power banks and portable devices often add a buck-boost circuit to either step down the voltage from a series-connected battery to power it via USB, or conversely, to step up the voltage from USB to power a series-connected battery.

In applications such as industrial ESS where single battery packs are stacked in series to form a multi-module, voltages ranging from several hundred volts to several thousand volts are formed.

To ensure safety, insulation must be provided between each battery module, and communication between each module must be performed in an isolated state. Additionally, a relay rather than a MOSFET is used as a protection switch.

This explains how to configure a MOSFET when used as a battery protection switch.

The protection circuit unit can be located near each + and - terminal of the battery.

+ When positioned close to the terminal, the ground level is the same, so there is no need to consider offset when controlling communication, etc. However, the MOSFET used in the protection circuit uses an N-Channel MOSFET, which has the disadvantage of requiring a gate driver with a charge pump function to be used because the gate terminal must always have a higher voltage than the source terminal.

If the protection circuit is placed close to the terminal, a charge pump is not required, but there is a part where the level changes on the left and right of the protection circuit, so separate isolation, etc. must be used for communication between the outside and the BMS module.

Explains how to connect battery protection switch MOSFETs, introducing back-to-back types of Common Source and Common Drain.

The advantage of Common Source is that the two switches are turned on/off with a single gate signal, so the switching operation is fast and relatively cheap. On the other hand, if there is a problem with one switch, it affects the entire MOSFET.

Common Drain means that the gate driver has two signals to drive each MOSFET. This is why one gate driver must have two charge pump functions. Each MOSFET can be driven separately, which provides excellent stability.

Director Yongjin Kim said that the most important parameter to consider when using MOSFETs in parallel is VGS(th).

As the difference in VGS(th) increases, the power loss flowing through each MOSFET increases. When VGS(th) differed by 1.6 V, it showed an 88% increase compared to 0 V.

When 6 MOSFETs are connected in parallel and fully turned on, there is no significant difference in conduction loss, but at the moment of turning on/off, the greater the VGS(th) deviation, the greater the loss.

Infineon's MOSFETs are said to have a smaller minimum and maximum difference in VGS(th) than competitors, which is advantageous in applications where multiple MOSFETs are used in parallel.

Next, Director Kim introduced Infineon’s BMS solution and said, “BMS often uses MOSFETs in parallel,” and “Customers often worry about how to solve the problem of increasing size when using MOSFETs in parallel.”

Due to these issues, customers are demanding products with smaller RDS(on) in smaller packages.

Infineon has two product lines: StrongIRFET and OptiMOS.

Director Kim explained that OptiMOS is suitable for BMS because it must have lower heat rise for higher discharge current while reducing size.

He added that if price competitiveness is sought, it is okay to use previous-generation products, but there is the problem that the number of parallel devices must increase.

Infineon's packages used in BMS are D2PAK, D2PAK 7pin, and D2PAK 7pin+.>
To reduce the package size, there is the TO-Leadless (TOLL) package, and the TOLT package that can cover high discharge current even with a small number of MOSFETs by connecting a heat sink to the top side.

If we reduce the size to 5 x 6, we can use SuperSO8 as protection MOSFET, and if we want to maintain parallel count in high current situation, we can use sTOLL package.

For small devices such as laptops, it is common to use a 3.3 x 3.3 package.

Common Source, Common Drain type MOSFETs used as battery protection switches must have low RDS(on), low thermal resistance, sufficient safe operating area, and strong tolerance in linear mode.

Director Yongjin Kim then explained the EiceDRIVER-2ED4820-EM driver for driving the MOSFET, the current sensor, and the BMIC for voltage and balancing the cell.

The EiceDRIVER-2ED4820-EM driver supports 20~70V and the current consumed by the IC in Sleep Mode is less than 5 microamperes. It has a built-in charge pump so it can drive N-Channel on the high side (+ terminal side), and since two gate signals are output, the MOSFET is connected to Common Drain.

Infineon has 20~300V low and medium voltage MOSFETs, and high voltage silicon MOSFET products such as 600V and 950V.

XENSIV Magnetic Current Sensor is available in three package types: △PG-TSON-8 △PG-VSON-6 △PG-TDSO-16.

PG-TSON-8 has the feature that the current rail passes through the chip, while the other two packages are external current rail.

The XENSIV Magnetic Current Sensor has two Over Current Detection functions and is powered by 3.3V.

It also provides protection functions equivalent to ASIL B for automotive applications.

In addition, Director Yongjin Kim introduced the TLE9012DQU and TLE9015DQU IC products and shared information about Infineon’s diverse product lines.

The webinar can be found at the link 'Understanding Battery Management System Components and Protection MOSFET Selection Criteria'.