Application Note Automotive communication interface: Products recommended for PoC use (PoC filter inductors, chip beads)

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The demand for high-speed automotive onboard interfaces is increasing, with a view towards supporting driving safety, reducing the environmental load, and improving comfort. For bidirectional communication, the automotive Ethernet format is commonly used, while LVDS is the choice for one-way communication. With LVDS (Low Voltage Differential Signaling), the preferred approach is to also adopt the PoC (Power over Coax) method that enables transmission of the signal and power supply over a single coaxial cable, thereby reducing the weight of wire harnesses in the car. This page describes usage examples and effects of inductors and chip beads specifically recommended for PoC filter applications.

Transfer system suitable for high-speed automotive interfaces

With the increasing speed and sophistication of interfaces in cars, the PoC (Power over Coax) approach is gaining in popularity, as it allows superimposing signals and power in one coaxial cable. TDK offers purpose-designed inductors for PoC filters which make it possible to achieve the required transfer characteristics while saving space.
PoC configurations make use of multi-inductance combinations to maintain high impedance over a broad frequency range, in order to separate the signal from the power supply.

Figure 1 PoC transfer system
PoC transfer system

High-speed and power ratings for LVDS-PoC

Sensing systems including cameras, radar and similar are evolving towards higher precision, which means that the amount of information which has to be handled increases, along with higher performance and functional complexity. Modules used for such systems therefore need to support high transfer speeds and high power ratings. Consequently, the PoC communication interface specifications are also shifting from 1.5Gbps to speeds in the 5Gbps range, and required power ratings are increasing from about 1W to about 5W.

Figure 2 Camera module for Autonomous-Driving / ADAS
Camera module for Autonomous-Driving / ADAS

Development of inductor (coil) optimized for PoC filter use

Realizing smaller dimensions (37% mounting footprint reduction)

Automotive camera modules and similar systems often are subject to severe space limitations, making compact product dimensions and smaller mounting footprints an important requirement.
A typical inductor configuration includes a four-piece combination of inductors and chip beads, but using the PoC purpose-designed inductors from TDK makes it possible to fulfill the same conditions with only one inductor and two chip beads.
This results in a mounting footprint reduction of about 37%.
When the number of inductors is reduced, it is necessary to select the components so that high impedance characteristics can be maintained over a broad frequency range.
At the same time, performance must be maintained and operation must be guaranteed up to high temperatures with a maximum of 150°C.

Figure 3 PoC filter configuration example
PoC filter configuration example
Table 1 TDK inductors recommended for PoC filter use

Example: 4Gbps 300mA PoC filter

Component Filter 1 Filter 2 Filter 3 Filter 4 Rdc[Ω] Mounting footprint
[mm²]
Recommended by TDK ADL3225VT-100M-TL000 / 1.2kΩ Chip Beads
MPZ1608S102ATD25
Chip Beads
MMZ1608Y152BTD25
N/A 1.05
-44%
15.83
-32%
General power supply circuit inductors NLCV32T-100K-EFRD/2kΩ NLCV25T-4R7M-EFRD/2kΩ Chip Beads
MPZ1608S102ATD25
Chip Beads
MMZ1608Y152BTD25
2.09 24.95

Maintaining required impedance characteristics over a wide range

Using PoC filter inductors of the ADL series makes it possible to maintain suitable impedance characteristics over a wide range.
Support for high current ratings is usually implemented by using multiple inductors, but selecting PoC filter inductors of the ADL series enables realizing the same goal with fewer components.
Compared to the use of conventional inductors, frequency ripples are reduced over a wide range.
In this way, TDK solutions help to realize flat frequency characteristics.

Figure 4 Effect of TDK inductors for PoC filter use
Effect of TDK inductors for PoC filter use

List of TDK inductors recommended for PoC filter use

TDK is advancing its lineup of inductors for PoC filters, as shown in Figure 5, according to allowable current and filter requirements (Table 2).
The MLJ1608-G series, which is compact and covers high-frequency bandwidth, contributes to the miniaturization of filters.
The ADL series supports a wide bandwidth, and using the ADL series can reduce the number of coils in the filter. Furthermore, development is underway for the ADL4524VL and ADL8030VA series, which cover an even wider bandwidth.
In addition, the development of the ADL4532VK and ADL3225VF series for high currents is progressing.

Figure 5 Types of inductors for PoC filter use
Types of inductors for PoC filter use

* R1 to R3 may vary according to the combination of capacitors and chip beads. Please inquire for details.

Table 2 TDK-recommended PoC filter configurations

Note: *** stands for the inductance value or impedance value. For details, please see the respective product specifications.

Max. Allowable
Current
Max. Ambient
Temperature※1
Filter 1 Filter 2 Filter 3 Applicable Speed / Frequency (*2)
(Reference value)
Product Name
Inductance / uH
(Typical value)
Parallel Resistance Product Name
Inductance / uH
(Typical value)
Parallel Resistance Product Name
Inductance / uH
(Typical value)
Parallel Resistance
300mA 105℃ VLS4020CX-101M-H
L=100±20%
1kΩ ADL2012-2R2M-T01
L=2.2±20%
- - - I2C / 1MHz or above
Video signal / 2Gbps or less
ADL3225V-470MT-TL000
L=47±20%
2kΩ MLZ1608CAC1R0MTD25
L=1.0±20%
(Developing)
- - - I2C / 1MHz or above
Video signal / 2Gbps or less
ADL3225VT-100M-TL000
L=10±20%
1.2kΩ ADL2012-2R2M-T01
L=2.2±20%
- - - I2C / 5MHz or above
Video signal / 7Gbps or less
400mA 105℃ VLS3015CX-220M-H
L=22±20%
1kΩ ADL2012-2R2M-T01
L=2.2±20%
- - - I2C / 2MHz or above
Video signal / 7Gbps or less
125℃ ADL4524VL-180M-TL000
(Developing)
- - - - - I2C / 2MHz or above
Video signal / 10Gbps or less
VLS5030EX-101M-D
L=100±20%
1kΩ ADL32VHC-100M
L=10±20%
1kΩ MLZ1608CDCR22MTD25
L=0.22±20%
(Developing)
- I2C / 1MHz or above
Video signal / 2Gbps or less
500mA 105℃ ADL32VHC-220M
L=22±20%
1kΩ MLJ1608WGCR56NTD25
L=0.56±30%
- - - I2C / 2MHz or above
Video signal / 10Gbps or less
VLS3015CX-220M-H
L=22±20%
1kΩ MLZ2012M1R5HTD25
L=1.5±20%
1kΩ MLJ1608WGCR56NTD25
L=0.56±30%
- I2C / 2MHz or above
Video signal / 7Gbps or less
600mA 105℃ ADL8030VA-220M
(Developing)
- - - - - I2C / 2MHz or above
Video signal / 10Gbps or less
ADL32VHC-150M
L=15±20%
1.5kΩ ADL2012-1R5M-T01
L=1.5±20%
- - - I2C / 2MHz or above
Video signal / 7Gbps or less
800mA 125℃ VLS5030EX-220M-D
L=22±20%
1.5kΩ ADL3225VM-2R2M-TL001
L=2.2±20%
1.5kΩ ADL3225VM-2R2M-TL001
L=2.2±20%
- I2C / 2MHz or above
Video signal / 7Gbps or less
1A 105℃ VLS5030EX-220M-D
L=22±20%
1.5kΩ ADL3225VM-2R2M-TL001
L=2.2±20%
1.5kΩ ADL3225VM-2R2M-TL001
L=2.2±20%
- I2C / 2MHz or above
Video signal / 7Gbps or less
1.5A 105℃ FLP5535-220M
(Developing)
1kΩ ADL4532VK-3R0M
(Developing)
1kΩ ADL3225VF-R49M
(Developing)
- I2C / 2MHz or above
Video signal / 7Gbps or less
  • <Reference>
  • ※1 Estimated current value that can be tolerated under our testing environment. It may vary depending on the environment in which it is used, so please use it within the temperature range that does not exceed the product specifications.
  • ※2 Applicable Speed / Frequency varies according to each standard value. Please contact us for details.