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[FAQ] How do you generate isolated power for an isolated RS-485 node?

How do you generate isolated power for an isolated RS-485 node?

  • There are several options to generate isolated power for an isolated RS-485 node; the best solution depends on the specific application needs.

    One option is to use a transformer driver like TI’s SN6501, which operates in a push-pull configuration with a transformer and optional rectifying low-dropout regulator (LDO) on the secondary side (Figure 1). The SN6501 is capable of delivering as much as 1.5W to provide isolated power. This device has the flexibility for use in almost all applications, because the transformer and turns ratio can provide the necessary isolation rating and output voltage for the power supply. You can use the SN6505 instead of the SN6501 for as much as 5W of output power if you need isolated power for additional devices. SN6505 has extra protection features such as overload and short circuit, thermal shutdown, soft start, and slew rate control enabling a robust solution.

    Figure 1: Isolated power for the ISO1410 using the SN6501

    Another option for space-constrained applications is the ISOW78xx family of devices, which provides signal and power isolation in a small-outline integrated circuit (SOIC)-16 package. The ISOW7841 can be combined with a non-isolated RS-485 transceiver, as shown in the Isolated RS-485 with Integrated Signal and Power Reference Design. This combination is compact; doesn’t require a transformer; and makes certifications easy. See all documentation available in the ISOW7841 online product folder for more information.

    Figure 2: Isolated RS-485 with integrated signal and power using the ISOW7841

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