Signal and power isolation RS-485 field bus high-speed or low-power solution

“ADI’s iCoupler® digital isolator and RS-485 transceiver product series address two major requirements in industrial applications: higher data rates and lower power consumption operating modes.

“

Introduction

ADI’s iCoupler® digital isolator and RS-485 transceiver product series address two major requirements in industrial applications: higher data rates and lower power consumption operating modes.

For high-performance motor control encoder applications, higher data rates, smaller RS-485 transceiver packages, and IEC 61000-4-2 ESD protection are usually required. The ADM3065E/ADM3066E 50 Mbps transceiver is housed in a space-saving 10-pin LFCSP package and can provide ±12 kV (contact) and ±12 kV (air) IEC 61000-4-2 ESD protection functions. It provides a A reliable solution (please refer to AN-1397 application note for more information). In addition, adding high-speed and stable signal and power isolation to the ADM3065E/ADM3066E can be achieved by isoPower® ADuM6401 or isoPower ADuM6000 and iCoupler ADuM241D, as described in this application note.

In battery-powered systems, downhole applications (for example, mining), and process control systems operating in a 4 mA to 20 mA loop, there is often a high demand for low-power operating modes. The static power consumption of the micro-power digital isolator ADuM1441 produced by ADI in shutdown mode is less than 23 μA. The static power consumption of the ADM3483 3.3 V, 250 kbps RS-485 transceiver is extremely low, typically only 2 nA in shutdown mode.

Figure 1 shows a stable and reliable low-power isolated RS-485 solution suitable for downhole applications. ADM3483 and ADuM1441 share a reliable low-power link to remote underground measurement nodes. The system interface card includes ARM® Cortex® microcontroller unit (MCU), ADuCM3027 and integrated analog front end (AFE) AD7124-4 for remote temperature and pressure measurement. The firmware update of the system interface card is provided through a long-distance RS-485 cable, which can realize low data rate transmission (for example, 9.6 kbps) within a long distance of up to 1 km after the update.

Figure 1. A stable and reliable low-power isolated RS-485 solution suitable for downhole applications

Isolated high-speed RS-485

Using iCoupler and isoPower technology, galvanic isolation with both reinforced insulation and 5 kV rms transient withstand voltage can be added to the ADM3065E. The ADuM6401 provides the required four-channel 5 kV rms signal isolation, a maximum operating rate of 25 Mbps, and an integrated DC/DC converter. ADuM6401 and ADM3065E (as shown in Figure 2) need to configure the VISO pin to 3.3 V. The specific method is to connect the VSEL pin to the GNDISO pin and the 5V power supply to the VDD1 pin. Working under 3.3V voltage, even if the data rate reaches 25 Mbps, it can ensure that the ADM3065E still remains within the load capacity of the ADuM6401.

Using ADuM241D four-channel digital isolator and ADuM6000 isolated DC/DC converter, 50 Mbps data rate and ADM3065E isolation can be achieved, as shown in Figure 3. The ADuM241D has a data rate of up to 150 Mbps and can provide the precise timing required to fully support the ADM3065E operating at a data rate of 50 Mbps.

However, the prerequisite for working at a data rate of 50 Mbps is to make the ADM3065E work at 3.3 V.

If you need to work at 5V, you can connect the VSEL pin on the ADuM6000 to VISO, but the maximum data rate supported will be reduced (for example,
The DC/DC converters in the ADuM6401 and ADuM6000 isoPower devices can provide regulated and isolated power for the ADM3065E (and ADuM241D). These two isoPower devices use high-frequency switching elements to transmit power through a transformer. Users must follow radiation standards for printed circuit board (PCB) layout. For PCB layout recommendations, please refer to the AN-0971 application note.

Isolated low-power RS-485

Figure 4 shows the combination of the ADuM1441 micropower, four-channel, digital isolator and the ADM3483 low-power, half-duplex RS-485 transceiver.

When the ADM3483 is in shutdown mode (driver enable DE pin is low and receiver enable pin is high), the quiescent supply current is usually only 2 nA (maximum specification value is 1 μA). As shown in Figure 4, pins 7 and 10 of the ADuM1441 are connected to GND1 and GND2, respectively. This means that when the ADuM1441 isolator is in shutdown mode with no bus communication activity, its quiescent current is less than 23 µA. Overall, the static power consumption of this solution is as low as 24 µA or less.

If pins 7 and 10 of the ADuM1441 are directly connected to VDD1 and VDD2, respectively, the static power consumption of the ADuM1441 is only 1.2 µA. This can be achieved through jumper connections on the PCB. The user can choose to connect pin 7 to VDD1 or GND1, and also choose to connect pin 10 to VDD2 or GND2. Adding the 1.2 μA static power consumption feature of the ADuM1441 to the ADM3483 static power supply allows a fully isolated RS-485 node that consumes only 2 μA in shutdown or standby mode. To ensure proper operation of the isolator, pin 7 and pin 10 of the ADuM1441 must be connected to GND1 and GND2, respectively.