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FAN3240TMX Folha de dados(PDF) 11 Page - Fairchild Semiconductor |
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FAN3240TMX Folha de dados(HTML) 11 Page - Fairchild Semiconductor |
11 / 19 page © 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN3240 • Rev. 1.0.2 11 2. Internal Bias Regulator (5VB Pin) The FAN324x’s internal bias generator is a low dropout linear regulator with a 5 V output. The regulator is designed to operate with minimum overhead; it is able to regulate its output with very low voltage drop across its bypass element. The 5 V output of the regulator can be used to power external circuitry as well. In addition to the internal power consumption of the FAN324x, the regulator can deliver at least 5 mA additional current for an external load connected to the 5VB pin of the device. Similar to other linear regulator circuits, the on-board regulator needs to be bypassed externally for stabile operation. It is recommended that the output of the regulator is bypassed by at least a 100 nF, good-quality, high-frequency, ceramic capacitor placed in close proximity to the 5VB and GND pins. 3. Enable Operation (EN Pin) The enable (EN) input is a level-sensitive input and it is the most dominant input of the FAN324x during normal operation. The enable pin must be above the input threshold to generate an output pulse and energize the relay coil. The input circuit of the enable input is comprised of a comparator circuit with a precise voltage source connected to the inverting input of the comparator and the EN pin connected to the non- inverting input. To avoid erroneous operation due to potential noise superimposed on the incoming control signal, the enable signal goes through a low-pass filter before it connects to the non-inverting input of the comparator. The filter is designed with a large time- constant; thus the enable input has an approximately 5 µs delay before it can act on the received command level. Once the EN pin is pulled LOW and the signal propagates through the filter, the relay drive outputs become high impedance and the internal control circuit returns to its initial inactive state. Time Base: 5 μs/div Figure 19. Enable Operating Waveforms Due to the precise thresholds, the EN input can also be used as a voltage monitoring input that enables or disables the relay drive based on the monitored voltage level. This functionality can be used to monitor other vital voltage levels in the system, such as the supply voltage for the logic generating the control signals for the FAN324x or the power rail of the relay being driven by the device. An example implementation of this monitoring functionality is shown in Figure 20. Internal Enable Signal 1.4V/1.3V 1 Filter 3.3V or VS EN pin Figure 20. Voltage Monitoring Example Using the EN Input Circuit As Figure 20 indicates, the input comparator is implemented with a fixed internal hysteresis of approximately 100 mV. The incoming low-pass filter and the built-in hysteresis of the comparator provide enough noise immunity to prevent inadvertent toggling of the internal enable signal. Additional filtering can be added by connecting an additional high-frequency capacitor between the EN pin and GND (pin 6). Since the input threshold of the comparator is compatible with TTL logic signal levels, the EN input can also be driven directly from a logic source, such as a microcontroller or other similar digital circuits. When the EN pin is driven by a logic signal, the resistors shown in Figure 20 are not needed and additional filtering is not required because of the fast rise and fall times of such digital signals. It is important to note that while the EN input is the most dominant input during normal operation, the Under- Voltage Lockout (UVLO) and Thermal Shutdown protection (TSD) override the enable input and can disable the operation of the device. 4. Input Signal Processing (IN1 and IN2 Pins) The FAN324x features two drive channels, one to energize the relay coil to close the relay contact(s) and another one to open it. The channels utilize their respective inputs (IN1 and IN2 pins) and outputs (OUT1 and OUT2 pins). Since the circuitry comprising the two driver channels inside the FAN324x are identical in implementation and in operation, they can be assigned to perform either the opening or closing functions. The voltage thresholds of the FAN324x inputs meet industry-standard TTL-logic levels independent of the supply voltage, VS. Therefore, the input pins can be driven from a range of logic signal levels for which a voltage over 2 V is considered logic HIGH (active). |
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