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TC670ECHTR Fiches technique(PDF) 6 Page - Microchip Technology |
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TC670ECHTR Fiches technique(HTML) 6 Page - Microchip Technology |
6 / 14 page TC670 DS21688D-page 6 2001-2012 Microchip Technology Inc. 4.0 DETAILED DESCRIPTION The TC670 is an integrated fan speed sensor that predicts/detects fan failure, consequently preventing thermal damage to systems with cooling fans. When the fan speed falls below a user-programmed threshold level, the TC670 asserts an ALERT signal. This threshold is set with an external resistor divider network. FIGURE 4-1: TC670 Block Diagram. As shown in Figure 4-1, the TC670 senses the fan pulses and internally converts those pulses from a frequency into an analog voltage. This voltage is then compared with the DC voltage at the THRESHOLD pin. If the converted frequency-to-voltage value from the fan's pulses falls below the threshold voltage, the ALERT output is pulled low. In a 3.0V system, the external fan alert level on the THRESHOLD pin can be designed from 0.0V (stalled fan) to 2.4V (for 13,000 RPM) to cover most of the com- mon fan speeds. This failure detection system works with linear-controlled 2-wire fans and eliminates the need for 3-wire fans. The TC670 can also work with 3-wire fans either by using the SENSE circuit or by directly sensing the RPM output from the 3rd wire. A CLEAR pin is provided to allow the user to reset the ALERT pin status back to a high state. This clear option also allows the flexibility of connecting the ALERT out- put of the TC670 with other alert/fault interrupts in the system without having a risk of a system shutdown due to false fan fault condition. FIGURE 4-2: Typical Application Circuit. 4.1 SENSE Input As shown in Figure 4-2, the SENSE input (Pin 6) is connected to the sense resistor (RSENSE) through a capacitor (CSENSE). The low value current sensing resistor (RSENSE) is connected between the ground return leg of the fan and the fan bias ground. During normal fan operation, commutation occurs as each pole of the fan is energized. This causes the fan current to be an AC waveform with fast falling edges. These short, rapid changes in fan current cause a corresponding dV/dt voltage across the sense resistor, as well as a corresponding dI/dt current through the sense capacitor. The current through CSENSE is termi- nated with the internal 50 k input resistance at the SENSE pin of the TC670. When positive-going fan pulses at the SENSE input are greater than 124 mV (typ.), the TC670 latches-in those voltage spikes. This 124 mV (typ.) SENSE input built-in threshold reduces false triggering errors caused by extraneous noise pulses associated with a running fan. The presence and frequency of these pulses is a direct indication of fan operation and fan speed. THRESHOLD 124 mV 50 k SENSE ALERT CLEAR Logic Frequency-to- Voltage GND VDD Bandgap Oscillator Note: This typical application circuit uses a LED to indicate that a fan failure has occurred. 5 6 CSENSE R4 RSENSE +12V ALERT LED DC FAN DC FAN SENSE ALERT 2 4 3 1 +5V R3 R2 0.1 µF VDD CLEAR THRESHOLD GND |
Numéro de pièce similaire - TC670ECHTR |
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Description similaire - TC670ECHTR |
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