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ISL72028SEHVX Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL72028SEHVX Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 19 page ISL72028SEH 10 FN8764.1 November 9, 2015 Submit Document Feedback Functional Description Overview The Intersil ISL72028SEH is a 3.3V radiation tolerant CAN transceiver that is compatible with the ISO11898-2 standard for use in CAN (Controller Area Network) serial communication systems. The device performs transmit and receive functions between the CAN controller and the CAN differential bus. It can transmit and receive at bus speeds of up to 1Mbps. It is designed to operate over a common-mode range of -7V to +12V with a maximum of 120 nodes. The device is capable of withstanding ±20V on the CANH and CANL bus pins outside of ion beam and ±16V under ion beam. Slope Adjustment The output driver rise and fall time has three distinct selections that may be chosen by using a resistor from the RS pin to GND. Connecting the RS pin directly to GND results in output switching times that are the fastest, limited only by the drive capability of the output stage. RS = 10kΩ provides for a typical slew rate of 8V/µs and RS = 50kΩ provides for a typical slew rate of 4V/µs. Putting a high logic level to the RS pin places the device in a low power shutdown mode. The protocol controller uses this mode to switch between low power shutdown mode and normal transmit mode. Cable Length The device can work per ISO11898 specification with a 40m cable and stub length of 0.3m and 60 nodes at 1Mbps. This is greater than the ISO requirement of 30 nodes. The cable type specified is twisted pair (shielded or unshielded) with a characteristic impedance of 120Ω. Resistors equal to this are to be terminated at both ends of the cable. Stubs should be kept as short as possible to prevent reflections. Cold Spare High reliability system designers implementing data communications have to be sensitive to the potential for single point failures. To mitigate the risk of a failure, they will use redundant bus transceivers in parallel. In this arrangement, both active and quiescent devices can be present simultaneously on the bus. The quiescent devices are powered down for cold spare and do not affect the communication of the other active nodes. To achieve this, a powered down transceiver (VCC < 200mV) has a resistance between the VREF pin or the CANH pin or CANL pin and the VCC supply rail of >480kΩ (max) with a typical resistance >2MΩ. The resistance between CANH and CANL of a powered-down transceiver has a typical resistance of 80kΩ. Low Power Shutdown Mode When a high level is applied to the RS pin, the device enters the low power shutdown mode in which the driver and receiver are switched off to conserve power. The bus pins are at High Z and R pin will be at logic high. In low power shutdown the transceiver draws 50µA (max) of current. A low level on the RS pin brings the device back to operation. Using 3.3V Devices in 5V Systems Looking at the differential voltage of both the 3.3V and 5V devices, the differential voltage is the same, the recessive common-mode output is the same. The dominant common-mode output voltage is slightly lower than the 5V counterparts. The receiver specs are also the same. Though the electrical parameters appear compatible, it is advised that necessary system testing be performed to verify interchangeable operation. Split Mode Termination The VREF pin provides a VCC/2 output voltage for split mode termination. The VREF pin has the same ESD protection, short circuit protection and common-mode operating range as the bus pins. The split mode termination technique is shown in Figure 19. It is used to stabilize the bus voltage at VCC/2 and prevent it from drifting to a high common-mode voltage during periods of inactivity. The technique improves the electromagnetic compatibility of a network. The split mode termination is put at each end of the bus. The CL capacitor between the two 60Ω resistors, filters unwanted high frequency noise to ground. The resistors should have a tolerance of 1% or better and the two resistors should be carefully matched to provide the most effective EMI immunity. A typical value of CL for a high speed CAN network is 4.7nF, which generates a 3dB point at 1.1Mbps. The capacitance value used is dependent on the signaling rate of the network. FIGURE 19. SPLIT TERMINATION NODE #1 NODE #n CANH CANL VREF VREF CL CL NODE #2 60Ω 60Ω 60Ω 60Ω |
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