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FAN3240TMX датащи(PDF) 10 Page - Fairchild Semiconductor |
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FAN3240TMX датащи(HTML) 10 Page - Fairchild Semiconductor |
10 / 19 page © 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN3240 • Rev. 0.1.5 10 Theory of Operation Polarized, bi-stabile, latching relays are utilized in many kinds of electronic equipment and diverse applications. These relays usually employ two coils; one to move the relay contact(s) from open to closed position and another coil to move the contact(s) from closed to open position. To facilitate the mechanical movement, the relay coils need to be energized for a specific time interval. Once the contact(s) have changed position, the voltage should be removed from the winding of the relay. A simplified, typical circuit diagram is shown in Figure 17 with example waveforms. Figure 17. Simplified Diagram of a Relay Drive As Figure 17 shows, a dual-coil relay is connected to its supply rail at the center point of the two relay windings. Each winding can be energized by the switches connected to the relay coils. The two switches must not be on at the same time because that would cause excessive currents drawn from the supply rail, VS. Furthermore, to accommodate the relatively long time required for the relay contact to travel between its stationary positions (ON and OFF positions), the pulse must be longer than the minimum duration specified in the relay datasheet. It is also desirable to limit the maximum length of the drive pulse to prevent potential saturation of the relay winding and to avoid over heating the coils and drive electronics. The relay specification also defines the minimum and maximum operating voltages for reliable operation of the contact(s). The FAN324x family of relay drivers is designed to minimize component count and board space, while increasing the reliability of the system and the noise immunity of the circuitry driving the coils of the relay. The integrated solution provides input signal qualification for the control signals, protection against simultaneous activation of the two relay coils, a maximum drive pulse duration limit, and many basic functions; such as monitoring the relay bias voltage (VS) for sufficient voltage level, driver enable input, and thermal protection for the IC. Functional Description 1. Powering the Device (VS Pin) The FAN324x device is powered through its VS pin by a single voltage source, which should be the same source powering the relay. In general, the VS pin should be connected to the highest potential in the system because the voltage stresses on all other pins shall not exceed the VS pin voltage by more than the forward- voltage drop of a P-N junction, as indicated in the Absolute Maximum Ratings table. During power-up, the FAN324x receives its bias voltage from the VS pin. As the voltage rises at the VS pin, the 5 V output internal bias regulator starts working. The voltage of the 5VB pin starts rising simultaneously with the bias voltage at the VS pin. Once the VS voltage is sufficiently high (as described below), the on-board linear regulator enters regulation and provides bias for the FAN324x internal circuitry. Due to the low power consumption of the internal control circuits; the on-board, low drop-out linear regulator is fully functional and in regulation from approximately 5.5 V on the VS pin. At this point, the FAN324x is still in under-voltage lockout (UVLO); i.e. the relay drive outputs are disabled and exhibit high impedance regardless of the status of the input and enable pins. The device becomes fully functional when the VS voltage exceeds the UVLO turn-on threshold and stays operational until the VS voltage falls below the UVLO turn-off threshold. The nominal UVLO hysteresis is about 1 V to prevent turning on and off the device due to noise when the VS voltage is near the UVLO threshold. The startup behavior is shown in Figure 18. Figure 18. Startup Waveforms As Figure 18 demonstrates, the startup behavior of the FAN324x devices are well controlled, the bias generator enters regulation smoothly without overshoot or oscillation, and the outputs remain high impedance during the entire startup interval. |
Аналогичный номер детали - FAN3240TMX |
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Аналогичное описание - FAN3240TMX |
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