SLLA418C May 2021 – July 2022 ISO1176 , ISO1176T , ISO1410 , ISO1412 , ISO1430 , ISO1432 , ISO1450 , ISO1452 , ISO15 , ISO1500 , ISO3080 , ISO3082 , ISO3086 , ISO3086T , ISO3088 , ISO35 , ISO35T , ISOW1412 , ISOW1432
RS-485 is one of the most widely used wired interface for industrial long-haul networks. TIA/EIA-485-A standard defines the physical layer of the RS-485 interface. End applications use RS-485 interface coupled with protocol such as Profibus, Modbus or BACnet. The main benefits of this interface include:
Applications for RS-485 include Energy Meters, Grid Protection relay, Solar inverter, Factory automation, Motor control and Heating, ventilation, air conditioning (HVAC) systems.
Figure 1-1 shows a typical block diagram of AC Motor drive:
A control module typically communicates to a Programmable logic controller (PLC) over RS-485 physical layer. It is common in factory environments that the ground potential difference (GPD) between the AC drive and the PLC can be much higher than the common mode voltage range suggested in the RS-485 standard. Galvanic isolation is usually introduced in the signal and supply lines of the RS-485 bus transceiver in the drive system to break to ground loop. This technique allows to transfer data between the drive and the PLC in the presence of huge GPD. In this case, basic isolation for RS-485 link is sufficient since high voltage in power stage is already isolated from control stage. Electrical fast transient (EFT) on the RS-485 link also becomes a key concern because of inductive switching.
Figure 1-2 shows typical implementation of a Solar Inverter. RS-485 serves as a communication channel between the Inverter and the control station. The configuration and performance parameters are transferred between the Control station and the inverter over the RS-485 link.
In Figure 1-2, control module that drives the inverter stage is referenced to High voltage DC-. RS-485 link is interfaced on a human accessible connector and must be protected from high voltage to account for operator safety, mandating reinforced isolation. With increasing demand for higher conversion efficiency, solar inverters are being designed with higher DC link voltages up to 1500 V. This translates to need for higher working voltage for the isolation barrier for RS-485 communication.
Other than isolation, key requirements of the systems requiring Isolated RS-485 are:
The ISO1410 is the latest Isolated RS-485/Profibus transceiver from Texas Instruments with all the above mentioned capabilities. Figure 1-3 shows the typical application schematic. This device can operate from 1.71 V to 5.5 V on the logic side, allowing to be interfaced with low voltage FPGAs and ASICs. Wide bus side supply voltage from 3 to 5.5 V eliminates the need for regulated supply voltage. This device family is fully characterized over a wide operating ambient temperature range from –40°C to +125°C and is available in 16-pin wide body SOIC package (8-mm creepage/clearance).
The SiO2 isolation barrier supports isolation withstand voltage of 5 kVRMS for 60 s per UL1577. It is available in basic and reinforced isolation options as shown in Table 1-1.
|Surge test voltage per VDE||10000 VPK||6000 VPK|
|Isolation rating per UL||5000 VRMS||5000 VRMS|
|Working voltage per VDE||1000 VRMS /1500 VPK||1000 VRMS /1500 VPK|
SiO2 based isolation barrier offers superior isolation performance that is resistant to temperature and humidity. Isolation working voltage of 1500 Vpk for 40 years lifetime is highest in the industry and allows to be used in 1500 V Solar Inverter and 690 VAC Motor drive systems.
Other differentiating features of ISO1410 are:
ISO1410 device offers integration along with superior system level performance. This device has highest working voltage (1500Vpk) in the industry and is capable to tolerate very high levels of IEC ESD and EFT.
These features make it a compelling solution for most industrial applications including Solar inverter and Motor drives. This device addresses key concerns often faced by end equipment designers in isolating RS-485 ports and enables communication in harsh industrial environments.
|Device||Optimized Parameters||Performance Trade-Off|
|ISOW1412||Optimized Parameters: 5-kVRMS, 500-kbps isolated RS-485 transceiver with integrated DC/DC converter||Performance Trade-off: Integrated low radiated emissions DC/DC converter reduces board space and simplifies designs|
|ISOW1432||Optimized Parameters: 5-kVRMS, 12-Mbps isolated RS-485 transceiver with integrated DC/DC converter||Performance Trade-off: Integrated low radiated emissions DC/DC converter reduces board space and simplifies designs|