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Fig. 2: Over-load and short-to-GND diagnostics per channel: the output current is monitored and if the current limitation of 1A (typically) is activated, then diagnostic feedback OCL is triggered. market provides integrated “open load” detection that is specific to any of the individual channels. Like with the overload detection, this greatly helps OEMs to reduce the time to identify the root cause of such a failure. Other channel-specific feedbacks Even before the switch is turned on, an open load (“wire-break”) can be detected. This is possible because in addition to monitoring the output current, the voltage at the output of the IC is also being monitored. In case of the output being in “off” state a small trickle current of 25μA is flown through the load. For loads with an ohmic resistance of less than 12 kOhm, if the output is disconnected from the load, the output will float at a voltage higher than 2V which in turn triggers the OLI diagnostic feedback (Open Load Current). The switch output could erroneously be connected to Vbb. Root causes may include wiring error, short-circuit during operation or a natural disaster which leaves the equipment flooded. This condition can also be detected by the ISO2H823V. Excessive heavy duty operation of outputs may be an indication for gradual degradation of the machinery on the factory floor. For this reason each of the output channels is equipped with an individual temperature sensor. When the output driver temperature reaches 150°C the respective output channel is automatically turned off to avoid material damage to the IC. Five types of diagnostics on IC-level Of all of the IC-level diagnostics, Vbb-monitoring is probably the most important one. Vbb-monitoring checks the voltage level on the driver’s output side. The possible reasons for this voltage failing and falling below the normal operation level could be that the power supply is not adequately designed for the loads, or the power supply is simply beginning to fail. It is also conceivable that the electrical connection between the power supply and the switching IC is gradually increasing its ohmic resistance, i.e. corrosion may be at work. In a large number of applications the nominal supply voltage (Vbb) on the factory side is 24V +/-20%. However, if that voltage drops to a level as low as 9V, the outputs are turned off while it is still possible to do so. This is not done without a pre-warning, as a matter of fact, there are two intermittent stages: If the supply voltage drops below 16V then an Under-Voltage warning UV is issued. At that voltage the performance level of outputs of the IC is not yet compromised. The UV feedback provides a pre-warning. If the supply voltage drops further, i.e. to a level of 13V and below, then a Missing Voltage warning MV is sent. At this supply voltage level, the IC outputs are still working. However one may be well advised to perform a controlled system shut-down while it is still possible. Only if the supply voltage drops to 9V or less, all outputs are automatically turned off and a Wait-for-Power W4P feedback is triggered. In this case the supply voltage has dropped to a level too low for proper operation - see figure 4. POWER COMPONENTS Fig. 3: Open load diagnostics per channel: the current across the switch is monitored and a threshold current can be selected from 0.5 to 3mA. If the current is below the threshold, then the diagnostic feedback OLA is triggered. Four additional IC-level feedbacks In addition to the temperature monitoring of each of the eight output channels, the IC has a ninth temperature sensor. This additional sensor provides on IC-level over temperature protection. The threshold is set to 125°C in order to remain below the glazing temperature of standard FR4 PCB materials. When this threshold is exceeded all outputs are automatically shut off (“OTP ”). While the ISO2H823V delivers compelling benefits over previous generation solutions, it must also be able to retrofit with factory automation systems which are not yet at the end of their operational life. The detection of the presence of an incandescent lamp (used for signaling purposes on the factory floor) is a requirement for many such legacy systems. The LAMP feedback permits the system controller to distinguish between turning on a cold incandescent bulb and a short-circuit. To attain uncompromised robustness against electro-magnetic interference the communication across the integrated galvanic isolation is save-guarded by multiple proprietary measures. In the unlikely event there were to be disturbance of that communication its occurrence would be flagged to the μC by way of setting the transmit error (“TE”) flag. If this error were to occur repetitively then it would indicate a substantial problem present on PCB-level. To verify system status, but also for safety reasons, it can be of importance to be sure that all outputs are in fact off. The IC provides such explicit “ALLOF ” feedback if indeed all outputs are off. Preventive diagnostics and full control With this impressive list of ten different types of diagnostic feedbacks, the ISO2H823V clearly sets a new standard in diagnostics for industrial control applications. The channel-specific diagnostic as well as the types of channel-specific diagnostic feedbacks can be enabled and disabled on a channel per channel basis. This grants the user the maximum of flexibility and allows the selective use these features to meet application specific requirements. Fig. 4: Various responses triggered under Vbb monitoring. 18 Electronic Engineering Times Europe May 2013 www.electronics-eetimes.com


EETE MAY 2013
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