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50 ADI | Engineering a More Sustainable Future Table 2. Power Inductor—Constraints on Package Size Parameter Implications for Inductor Package Size LPD5030- 224MRB Value Comment Sufficiently High Inductance Higher inductance values result in more internal windings and larger package size. 220 µH ±20% Recommended PoDL inductance. Higher SRF ( Self-Resonant Frequency ) Higher SRF will mean less internal windings and smaller size. 5.53 MHz Larger than the maximum 10 Mbps data rate on the 10BASE-T1L link. Higher Rated and Saturation Current Less internal windings, but larger package size.w 0.24 A, 0.31 A Exceeds 10BASE-T1L MEMS sensor requirements. Low DCR To achieve lower DCR, wires need to be thicker and have fewer windings. 3.3 Ω Hard to have thicker windings in a smaller package. Figure 2. Basic principles of shared power and data wires (PoDL). The coupled inductor rated current needs to meet or exceed the total current requirements for the remotely powered MEMS sensor node. The LPD5030-224MRB is rated to at least 240 mA, greatly exceeding the requirement for a 10BASE-T1L sensor node. As the rated current requirement is relatively low, the inductor size can be reduced. Table 2 shows that the 4.8 mm × 4.8 mm LPD5030- 224MRB is the smallest component that satisfies the 10BASE-T1L link requirements. How Do I Check if My PoDL Circuit Will Work? The IEEE 802.3cg-2019 standard for 10BASE-T1L outlines electrical specifications for a PHY to meet, including voltage levels, timing jitter, power spectral density, return loss, and signal droop ( decay ) . The PoDL circuit affects the communication channels, with return loss and signal decay ( or droop ) being two significant factors. Return loss is a measure of signal reflections likely to occur on a network and is caused by impedance mismatches at all locations along a cable link. Return loss is expressed in decibels and is of particular concern for high data rate or long cable reach ( 1700 m ) communications used in 10BASE-T1L. Figure 3 ( based on the work of Graber 1 ) shows an LTspice ® simulation circuit for the single-pair Ethernet ( SPE ) 10BASE-T1L standard ( 10SPE ) physical layer or MDI. The simulation circuit includes termination resistance of 100 Ω ±10% for Analog Devices' ADIN1110 or ADIN1100 2 Adobe Stock / WilliamJu – stock.adobe.com Adobe Stock / 安琦 王 – stock.adobe.com