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TC652FAVUA Arkusz danych(PDF) 6 Page - Microchip Technology |
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TC652FAVUA Arkusz danych(HTML) 6 Page - Microchip Technology |
6 / 14 page TC652/TC653 DS21453B-page 6 © 2002 Microchip Technology Inc. 3.2 Start-Up Timer To ensure reliable fan start-up, the Start-up Timer turns PWM high for about 2 seconds whenever the fan is started from the off state. This occurs at power-up and when coming out of Shutdown mode. 3.3 SENSE Input (FanSense™ Technology) The SENSE input, Pin 5, is connected to a low value current sensing resistor in the ground return leg of the fan circuit through the capacitor. During normal fan operation, commutation occurs as each pole of the fan is energized. This causes brief interruptions in the fan current, seen as pulses across the sense resistor. If the device is not in Shutdown mode, and pulses are not appearing at the SENSE input, a FAULT exists. The short, rapid change in fan current (high di/dt) causes a corresponding dv/dt across the sense resistor, RSENSE. The waveform on RSENSE is differentiated and con- verted to a logic-level pulse-train by CSENSE and the internal signal processing circuitry. The presence and frequency of this pulse-train is a direct indication of fan operation. 3.4 FAULT This pin goes low to indicate a fan FAULT condition. Pulses appearing at SENSE pin due to the PWM turn- ing on are blanked and the remaining pulses are filtered by a Missing Pulse Detector. If consecutive pulses are not detected for 32 PWM cycles (about 2 sec), the PWM is Low and FAULT goes low. FAULT can be disabled by momentarily toggling SHDN or VDD pin, or cycling system power. FAULT remains high during Shutdown mode. 3.5 Over-Temperature Alert (TOVER) This pin goes low when the TH set point is exceeded by 10°C (typical). This indicates that the fan is at maximum drive, and the potential exists for system overheating: either heat dissipation in the system has gone beyond the cooling system's design limits, or some FAULT exists such as fan bearing failure or an airflow obstruction. This output may be treated as a “System Overheat” warning and used to trigger system shutdown, or bring other fans to full speed in the system. The fan will continue to run at 100% speed while TOVER is asserted. Built-in hysteresis prevents TOVER from “chattering” when measured temperature is at or near the TH + 10°C trip point. As temperature falls through the TH + 10°C trip point, hysteresis maintains the TOVER output low until measured temperature is 5°C above the trip point setting. 3.6 Shutdown (SHDN) The fan can be unconditionally shutdown by pulling low the SHDN pin. During shutdown, FAULT output is high and PWM output is low. This is ideal for notebook computers and other portable applications when you need to change batteries and must not have the fan running at that time. Thermal monitoring and TOVER are still in operation during shutdown. IDD shutdown current is around 50 µA. 3.7 Auto-Shutdown Mode The TC653 has auto-shutdown. If the temperature is below the factory set point at minimum speed (TL), PWM is low and the fan is automatically shut off (Auto- shutdown mode). This feature is ideal for notebook computers and other portable applications that need to conserve as much battery power as possible and thus run a fan when it is only absolutely needed. The TC653 will continue to be active so as to monitor temperature for TOVER. The TC653 exits Auto-shutdown mode when the temperature rises above the factory set point (T1). 3.8 Temperature Selection Guide (Minimum Fan Speed/Full Speed) The five temperature regions defined by the six thresholds are defined in the TC652/TC653 by means of factory trimming. Once a TL and TH are set, the T1 – T4 thresholds are automatically equally spaced between TL and TH. |
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