Single Pair Ethernet: How to implement 10Base-T1L

Definition and Standards

Industrial Ethernet can easily be mixed up with regular Ethernet in industrial applications and will sometimes be called Single Pair Ethernet (SPE). This architecture is derived from standards known in classic LAN applications where two or four twisted pairs of wires are used to transmit data with either 100 Mbps (Megabit per second) or 1000 Mbps. SPE is using only one twisted pair of cables and is used for communication speeds ranging from 10 Mbps to 10 Gbps, each one following a dedicated standard (Table 1).

Table 2 shows the different power classes according to IEEE802.3cg table 104-1 as well as IEEE 802.3bu table 104-1a. The lowest power is specified with class 10 with a maximum current of 92mA flowing at the power interface resulting in a maximum average power for the powered device of 1.23W. The maximum power is specified with class 15 with a respective current of 1579mA and a maximum average available power of 52W for the powered device.

System architecture

There are different architectures possible defined by the applications power demand and safety requirements.
The first option is to use 10Base-T1L only for data transmission between control and sensing or acting element therefore only a common mode choke (CMC) is needed (Figure 1).

The second option includes the transmission of power which requires a common mode choke (CMC) and a differential mode inductor (DMI). The differential mode inductor can be selected according to the required power level or current being transmitted which will result in various options for the DMI. For higher currents bigger inductors have to be used and in sensing or acting devices where smaller currents are applied inductors with a lower height and smaller footprint might be preferred (Figure 2).

The third option is needed for areas which might be safety critical and where a galvanic isolation is required. For these environments, an isolating transformer or coupled inductor is used in addition to the CMC and the DMI to prevent unwanted currents to flow between the two devices (Figure 3).

In reality, all of the above options are needed, Figure 4 shows an implementation example starting at the top with the systems installed in the control room. Normally there is no need for isolation but common mode chokes and potentially differential mode inductors are used. Since there is a connection to backbone services and sometime cloud connection multiple speed levels (up to 1 Gbps) and technologies (e.g. 10Base-T1S, 100Base-T1, 100Base-TX, 1000Base-T) are used.
The next level is the near field where the different field switches are connected. For this application a cable length of several hundred meters up to 1000 m will be used, isolation is mandatory and common mode filters as well as DMIs for power sources with high power capability is needed.
In the last section the connection from the field switch towards sensors and actuators are realized. The requirements are similar to the previous level but the DMIs used in the loads could be of smaller size as the power consumption per device is normally in the range of up to 300 mA.

Circuitry

· Additional components

To reduce the impact of possible ESD pulses there are a few components useful. Bidirectional TVS-Diodes have the advantage of a low capacity and therefore can be used in high-speed applications. Also, they are fast, which increases the response time to high-voltage events.
Capacitors are used to prevent current from flowing through one coil of the Isolated Coupled Inductor and therefore reduce unnecessary power losses. Also, an additional isolation is added to ensure the usage in safety relevant environments.

· Setup for power class 10-14

The current defined for power classes 10 to 14 will be up to approx. 600 mA and for these scenarios a so called PHY-Side injection will be applied which means that the current injection and therefore the DMI will be placed between the PHY and the CMC, therefore the CMC has to withstand the current.

Circuit

BOM

No	Product Type	Value	TDK Part Number
C1, C2	Capacitor	100nF, 100V	CGA4J2X7R2A104K125AA
D2, D3	TVS Diode	5VDC, 15kV. 0.65pF	B74121U0033M060
I1	Isolated Coupled Inductor	2.2mH, 500mA, 2kV	ICI70CGI-222
L1	Common Mode Choke	470μH, 700mA 250μH, 100mA	RCM70CGI-471 ADF45CGI-251
L2	Inductor	250μH, 220mA	PID75-251M

· Setup for power class 15

The current defined for power class 15 is much higher than in any other class with approx. 1500 mA. For this scenario, if a line-side injection will be used which means that the power injection and therefore the DMI will be placed between the CMC and the connector. In this case the CMC can be designed much smaller as it does not have to work with the power being transmitted only with the signals.

Circuit

BOM

No	Product Type	Value	TDK Part Number
C1, C2	Capacitor	100nF, 100V	CGA4J2X7R2A104K125AA
D2, D3	TVS Diode	5VDC, 15kV. 0.65pF	B74121U0033M060
I1	Isolated Coupled Inductor	2.2mH, 500mA, 2kV	ICI70CGI-222
L1	Common Mode Choke	470μH, 700mA 250μH, 100mA	RCM70CGI-471 ADF45CGI-251
L2, L3	Inductor	470μH, 1800mA	PIS150H-471

Product Lineup

Table 3 shows the product lineup of TDK. It consists, as shown in the circuit diagram in Figure 3, of an Isolated Coupled Inductor, as well as a Common Mode Choke and a Power Inductor. The Power Inductors each refer to a power class as specified in table 2. Also, the APL power classes are shown in table 3.

Related Links

Product Portal