Necessity of Higher Voltage and Insulation System in Vehicle Electrification

Take the inverter circuit used in automobiles as an example. DC of AC becomes a circuit that converts to DC(1 next side) send a control signal from MOSFET, IGBTs, SiCs Before the switch circuit such as AC(2 next side) There are many cases where insulation is required for circuits that output .

Along with the recent electrification, the electric power [W] required for drive motors is increasing.

One of the methods to increase power is to increase the voltage. The primary side, which is the transmission side of the control signal, has a low voltage, and the secondary side, which is applied with the driving voltage / current including the switch circuit, has a high voltage. Voltage configuration is taken.

The following advantages can be obtained by insulating the primary and secondary sides, which handle different voltages.

① Ensuring safety

Since the circuit to which high voltage is applied is insulated, it is possible to separate the circuit that sends the control signal from the high voltage system.

In some cases, the insulation grade differs as a safety standard depending on how many volts the high voltage is in the application considering safety.

Satisfying the safety standards will also be an advantage in terms of reliability.

(2) GND loop can be divided

The primary (low voltage) and secondary (high voltage) GNDs are not shared, allowing independent GND loops.

This makes it possible to separate the circuit that transmits the primary-side control signal from the secondary-side circuit, which is a source of noise that can cause malfunctions.

Advantages of Infineon current sensors

Advantages of coreless current sensors

Infineon 's current sensor is a coreless method and can detect current in an insulated state, so there are two advantages: the advantage of the coreless method itself + the advantage of simplifying the insulation mechanism.

Other current detection methods include a shunt resistor method and a method with a core. The figure below shows a comparison with the coreless method.

method	merit	Demerit
Coreless	Size can be reduced (because no magnetic core is required) low heat Enables simplification of insulation design Capable of detecting current on both busbar and board	In some cases, the mechanism design becomes complicated.
with core	low heat Enables simplification of insulation design	Large size, heavy weight It is necessary to consider the characteristics of the magnetic core itself Only busbar current can be detected
shunt resistor	Extensive market experience	A thermal design that considers heat generation is required to pass current through the shunt resistor. No busbars required Requires signaling through isolation devices

Isolation Current Sensing

A feature of Infineon's current sensor is that it can detect current in an insulated state.

The concept of insulation differs depending on whether the current path to be measured flows inside the package or detects the current flowing outside the package, but we will introduce the multiple types of current paths and how to mount the current sensor IC below. .

Mounting method by current range

I explained that there are multiple mounting methods, but they are divided according to the current range of the measured current.

① "Soldered" on iCR PCB

Current Range: ~120A

Overview: A method of passing current inside a package and detecting current

Isolation: Inside the package, the Hall element is placed in a place that is insulated from where the current flows.

Proposable package: TISON-8

 

② "Soldered" onto the eCR PCB

Current Range: ~200A

Overview: How to "solder" a sensor onto a PCB and sense the current flowing through it

Isolation: Any terminal "soldered" to the PCB that is above the current path must be

It is a terminal that is unnecessary for the function as a sensor, and it is for fixing the sensor.

Insulation measurement is possible because the terminals that are out of the current path are the input and output terminals.

Proposable package: TDSO-16

 

③ eCR busbar parallel

Current Range: ~400A

Overview: A method for detecting the current flowing through the busbar outside the sensor

The positional relationship between the busbar and the sensor is arranged in parallel

Insulation: Mechanically, there is a spatial distance between the sensor and the busbar

Proposable package: TDSO-16/VSON-6

 

④ eCR busbar vertical

Current range: 400A~

Overview: How to insert the sensor vertically into the busbar against the busbar outside the sensor

Insulation: Mechanically, there is a spatial distance between the sensor and the busbar

Proposable package: VSON-6

 

*iCR: A method that detects the current by passing it through the package

*eCR: A method that detects the current flowing outside the package

Mechanism design required for current detection

In the previous article, we introduced four types of mounting methods.

Therefore, a magnetic shield is not necessary, but in order to achieve this, some mounting methods require additional mechanical design.

"Soldered" onto the eCR PCB

The figure below is an example of a type that is "soldered" onto the PCB with current sensing outside the package.

The red part in the upper half is the current path to be measured, and the thin red line in the lower part of the figure is the signal line.

There is a black slit in the current path to be measured, but if you add this, the current will curve (yellow arrow) and a magnetic field will be generated in the vertical direction of the figure, and it will be detected by the Hall element in the IC directly above. .

Example of "soldered" layout on eCR PCB

eCR busbar parallel

The figure below shows an example layout of a type in which the sensor board is arranged parallel to the bus bar, and a schematic diagram of the detection mechanism for current detection outside the package.

Similar to the "soldered" type on the PCB above, you will need to add slits to the busbar to curve the current.

The above type is the same, but these two slits have two Hall elements inside the IC, so that the magnetic flux is perpendicular to each.

eCR busbar parallel type layout example and detection mechanism

eCR busbar vertical

The figure below shows an example layout of a type in which a sensor is inserted perpendicularly to the bus bar, and a schematic diagram of the detection mechanism for current detection outside the package.

For this type, a hole for inserting the sensor is made in the center of the bus bar as shown in the lower right figure.

The structure is such that the elliptical magnetic field generated around the bus bar enters the two hall elements inside the package.

 

Example of eCR busbar vertical type layout and detection mechanism

Support during mechanical design

As mentioned earlier, it is necessary to make slits in the current paths of the busbar, PCB, etc., which slightly increases the resistance of the current path. It is also possible to verify by simulation how the

There is also a simulation tool for mechanism design on the Infineon​ ​web page, so please make use of it.

Of course, we can also discuss the necessary verification items for insulation, so please feel free to contact us.

Simulation tool for current sensor mechanism design

Evaluation Board

We have a lineup of evaluation boards for each configuration, a type that detects the current flowing inside the package (iCR) and a type that detects the current outside the package (eCR).

Please check the "current sensor product page" link below for information on this.

As an evaluation board, there are a programmer kit for rewriting the settings of the EEPROM built into the sensor as desired in the evaluation environment, and a board with the sensor actually installed.

As a function of the sensor, you can arbitrarily change the gain setting and overcurrent threshold setting, so please use the programmer kit.

The sensor-equipped board can detect current simply by connecting a harness, etc., so you can further omit the effort of performance evaluation.

New product TLE4972: 3.3V drive coreless current sensor (automotive standard compliant product)

Among the detection types introduced so far, we will finally introduce the new product "TLE4972" that was released as a type that detects the current outside the package.

[Product Features]

Wide measurement range: 0 to 31mT (0A to 2000A)
●3.3V operating voltage
●Analog output (single-ended, quasi/fully differential output)
●High bandwidth (typ. 210kHz) for high-speed measurement
●Differential measurement resistant to external disturbances due to two built-in Hall elements
●Built-in high-speed and two-system overcurrent detection function
High-accuracy current sense independent of age and temperature
-Built-in temperature sensor and stress sensor
●Various parameters can be set by built-in EEPROM
●ISO26262 compliant: ASIL-B compatible

Click here for the TLE4972　TDSO-16 package datasheet

TLE4972　VSON-6 package datasheet here

Buy at Macnica-Mouser

Inquiry/Quotation

In addition to this product, we also handle various sensor products and other product groups, so please refer to the link below.

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