ISO1050DUBR is digital Isolators from texas instruments.
Product Attribute :
Number of Channels : 1 Channel
Polarity : Unidirectional
Data Rate : 1 Mb/s
Isolation Voltage : 2500 Vrms
Isolation Type : Capacitive Coupling
Supply Voltage - Max : 5.5 V
Supply Voltage - Min : 3 V
Operating Supply Current : 52 mA
Propagation Delay Time : 74 ns
Operating Temperature : -55°C ~ 105°C
Applications :
• Industrial automation, control, sensors, and drive systems
• Building and climate control (HVAC) automation
• Security systems
• Transportation
• Medical
• Telecom
• CAN bus standards such as CANopen, DeviceNet, NMEA2000, ARINC825, ISO11783, CAN Kingdom, CANaerospace
Description :
The ISO1050 is a galvanically isolated CAN transceiver that meets the specifications of the ISO11898-2 standard. The device has the logic input and output buffers separated by a silicon oxide (SiO2) insulation barrier that provides galvanic isolation of up to 5000 VRMS for ISO1050DW and 2500 VRMS for ISO1050DUB. Used in conjunction with isolated power supplies, the device prevents noise currents on a data bus or other circuits from entering the local ground and interfering with or damaging sensitive circuitry.
As a CAN transceiver, the device provides differential transmit capability to the bus and differential receive capability to a CAN controller at signaling rates up to 1 megabit per second (Mbps). The device is designed for operation in especially harsh environments, and it features cross-wire, overvoltage and loss of ground protection from –27 V to 40 V and overtemperature shutdown, as well as –12V to 12V common-mode range.
The ISO1050 is characterized for operation over the ambient temperature range of –55°C to 105°C.
Overview :
The ISO1050 is a digitally isolated CAN transceiver with a typical transient immunity of 50 kV/µs. The device can operate from a 3.3-V supply on side 1 and a 5-V supply on side 2. This is of particular advantage for applications operating in harsh industrial environments because the 3.3 V on side 1 enables the connection to low-volt microcontrollers for power preservation, whereas the 5 V on side 2 maintains a high signal-to-noise ratio of the bus signals.
The CAN bus has two states during operation: dominant and recessive. A dominant bus state, equivalent to logic low, is when the bus is driven differentially by a driver. A recessive bus state is when the bus is biased to a common mode of VCC / 2 through the high-resistance internal input resistors of the receiver, equivalent to a logic high. The host microprocessor of the CAN node will use the TXD pin to drive the bus and will receive data from the bus on the RXD pin.
The device has several protection features that limit the short-circuit current when a CAN bus line is shorted.
These include driver current limiting (dominant and recessive). The device has TXD dominant state time out to prevent permanent higher short-circuit current of the dominant state during a system fault. During CAN communication the bus switches between dominant and recessive states with the data and control fields bits, thus the short-circuit current may be viewed either as the instantaneous current during each bus state, or as a DC average current. For system current (power supply) and power considerations in the termination resistors and common-mode choke ratings, use the average short-circuit current. Determine the ratio of dominant and recessive bits by the data in the CAN frame plus the following factors of the protocol and PHY that force either recessive or dominant at certain times:
• Control fields with set bits
• Bit-stuffing
• Interframe space
• TXD dominant time-out (fault case limiting)
These ensure a minimum recessive amount of time on the bus even if the data field contains a high percentage of dominant bits.
Application Information :
ISO1050 can be used with other components from TI such as a microcontroller, a transformer driver, and a linear voltage regulator to form a fully isolated CAN interface.
From Texas Instruments Datasheet
Design Requirements :
Unlike an optocoupler-based solution, which needs several external components to improve performance, provide bias, or limit current, ISO1050 only needs two external bypass capacitors to operate.
The ISO11898 Standard specifies a maximum bus length of 40 m and maximum stub length of 0.3 m with a maximum of 30 nodes. However, with careful design, users can have longer cables, longer stub lengths, and many more nodes to a bus. A high number of nodes requires a transceiver with high input impedance such as the ISO1050.
Many CAN organizations and standards have scaled the use of CAN for applications outside the original ISO11898 standard. They have made system level trade offs for data rate, cable length, and parasitic loading of the bus. Examples of some of these specifications are ARINC825, CANopen, CAN Kingdom, DeviceNet and NMEA200.
A CAN network design is a series of tradeoffs, but these devices operate over wide –12-V to 12-V commonmode range. In ISO11898-2 the driver differential output is specified with a 60-Ω load (the two 120-Ω termination resistors in parallel) and the differential output must be greater than 1.5 V. The ISO1050 is specified to meet the 1.5-V requirement with a 60-Ω load, and additionally specified with a differential output of 1.4 V with a 45-Ω load. The differential input resistance of the ISO1050 is a minimum of 30 kΩ. If 167 ISO1050 transceivers are in parallel on a bus, this is equivalent to a 180-Ω differential load. That transceiver load of 180 Ω in parallel with the 60 Ω gives a total 45 Ω. Therefore, the ISO1050 theoretically supports over 167 transceivers on a single bus segment with margin to the 1.2-V minimum differential input at each node. However for CAN network design margin must be given for signal loss across the system and cabling, parasitic loadings, network imbalances, ground offsets and signal integrity thus a practical maximum number of nodes is typically much lower. Bus length may also be extended beyond the original ISO11898 standard of 40 m by careful system design and data rate tradeoffs. For example, CAN open network design guidelines allow the network to be up to 1km with changes in the termination resistance, cabling, less than 64 nodes and significantly lowered data rate.
This flexibility in CAN network design is one of the key strengths of the various extensions and additional standards that have been built on the original ISO11898 CAN standard. In using this flexibility comes the responsibility of good network design.
CAN Termination
The ISO11898 standard specifies the interconnect to be a single twisted pair cable (shielded or unshielded) with 120-Ω characteristic impedance (ZO). Resistors equal to the characteristic impedance of the line should be used to terminate both ends of the cable to prevent signal reflections. Unterminated drop-lines (stubs) connecting nodes to the bus should be kept as short as possible to minimize signal reflections. The termination may be in a node, but if nodes may be removed from the bus, the termination must be carefully placed so that it is not removed from the bus.
From Texas Instruments Datasheet
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