TC670

TC670 Tiny Predictive Fan Failure Detector Features • Fan Wear-out Detection for 2-Wire Linear Controlled Fans • Replacement System for 3-Wire Fans • Fan Alert Signal when Fan Speed is below Programmed Threshold • CLEAR Capability for Eliminating False Alarm • Low Operating Current, 90µA (typ.) • VDD Range 3.0V to 5.5V • Available in a 6-Pin SOT-23 Package General Description The TC670 is an integrated fan speed sensor that predicts and/or detects fan failure, preventing thermal damage to systems with cooling fans. When the fan speed falls below a user specified level, the TC670 asserts an ALERT signal. With this design, a critical minimum fan speed is determined by the user. The fan alert level is then set with a resistor divider on the THRESHOLD pin (Pin 1) of the TC670. When the minimum fan speed is reached, the ALERT pin (Pin 5) changes from a digital HIGH to LOW. This failure detection works with all linear controlled 2-wire fans. The TC670 eliminates the need for 3-wire fan solutions. A CLEAR option can be used to reset the ALERT signal, allowing the flexibility of connecting the ALERT output of the TC670 with other Alert/FAULT interrupts in the system. This feature can be implemented so that false Fan Fault conditions do not initiate system shutdown. The TC670 is specified to operate over the full industrial temperature range of -40°C to +85°C. The TC670 is offered in a SOT23-6 pin package and consumes 90µA (typ) during operation. The space saving package and low power consumption make this device an ideal choice for systems requiring fan speed monitoring. Applications • • • • • • • Protection for Linear Controlled Fans Power Supplies Industrial Equipment PCs and Notebooks Data Storage Data Communications Equipment Instrumentation Device Selection Table Part Number TC670ECH Package 6-Pin SOT-23 Temp. Range -40°C to +85°C Typical Application Circuit +5V Package Type SOT-23A-6 TC670ECH THRESHOLD GND CLEAR 1 2 3 6 5 4 SENSE ALERT VDD 4V DD 0.1 µ F 3 From R3 Microcontroller 1 ALERT LED R4 CLEAR ALERT 5 DC FAN +12V R2 CSENSE THRESHOLD 6 SENSE GND 2 RSENSE 2002 Microchip Technology Inc. DS21688B-page 1 © TC670 1.0 ELECTRICAL CHARACTERISTICS Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections of the specifications is not implied. Exposure to Absolute Maximum Rating conditions for extended periods may affect device reliability. Absolute Maximum Ratings* VDD...................................................................................6.0V All inputs and outputs w.r.t. ..... (GND − 0.3V) to (VDD + 0.3V) Difference Input voltage ...................................... IVDD - GND Output Short Circuit Current ..................................continuous Current at Input Pin ................................................... +/-2 mA Current at Output Pin .............................................. +/-25 mA Junction Temperature, TJ ............................................. 150°C ESD protection on all pins ..................................................≥ 4 kV Operating Temperature Range........................-40°C to +85°C Storage Temperature Range .........................-55°C to +150°C TC670 ELECTRICAL SPECIFICATIONS Electrical Characteristics: Unless otherwise specified, all limits are specified at +25°C, VDD = 3.0V to 5.5V, CLEAR = Low. Boldface type specifications apply for temperature range of -40°C to +85°C Symbol Power Supply: VDD IDD CLEAR Input: VIH VIL SENSE Input: VTH(SENSE) RSENSE SENSE Input Level Threshold Voltage SENSE Input Resistance THRESHOLD Input Voltage Minimum THRESHOLD Input Voltage Maximum THRESHOLD Input Resistance ALERTACC VLOW tDELAY Note 1: Parameters Min Typ Max Unit Conditions Supply Voltage Supply Current CLEAR Logic Input High Level CLEAR Logic Input Low Level 3.0 — 0.8VDD — — — — — — (1) — 90 — — 124 50 0.0 2.4 100 — — 176 5.5 150 — 0.2VDD — — — — — +10 0.3 — V µA V V mV kΩ V V MΩ % V ms VDD = 3.0V ISINK = 2.5 mA THRESHOLD Input: Programmed Fan Speed Alert Accuracy ALERT Output Low Voltage ALERT Output Delay Time -10 — — ALERT Output: The TC670 will operate properly over the entire power supply range of 3.0V to 5.5V. As VDD varies from 3.0V, accuracy will degrade based on the percentage of VDD as shown in Section 3.0. TEMPERATURE SPECIFICATIONS Electrical Characteristics: Unless otherwise specified, all limits are specified for -40°C to +85°C and VDD = 3.0V to 5.5V Symbol Temperature Ranges: TA TA θJA Specified Temperature Range Operating Temperature Range Thermal Resistance, 6L-SOT-23 -40 -40 — — — 230 +85 +85 — °C °C °C/W Parameters Min Typ Max Unit Conditions Thermal Package Resistances: © DS21688B-page 2 2002 Microchip Technology Inc. TC670 2.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 2-1. TABLE 2-1: Pin No. (6-Pin SOT-23) 1 2 3 4 5 PIN FUNCTION TABLE Symbol Description THRESHOLD Analog Input used to set Fan ALERT Threshold Voltage. Input range = 0.0V to 2.4V. GND CLEAR VDD ALERT Ground Terminal. Digital Input. Active High. The ALERT Output is cleared when a high level signal is applied to this input. Power Supply Input, 3.0V to 5.5V. Digital (Open Drain) Output, active low. This pin goes low to indicate an alert condition when the fan speed at the SENSE pin reaches the alert threshold applied on the THRESHOLD pin. Analog Input. Current spikes are detected at this pin as the fan excitation signal transitions from high to low and low to high. 6 SENSE 2002 Microchip Technology Inc. DS21688B-page 3 © TC670 3.0 Note: TYPICAL PERFORMANCE CHARACTERISTICS The graphs and tables provided following this note are a statistical summary based on a limited number of samples and are provided for informational purposes only. The performance characteristics listed herein are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified operating range (e.g., outside specified power supply range) and therefore outside the warranted range. Supply Current IDD vs. Supply Voltage (VDD) vs. Temperature (TA) 115 110 105 SUPPLY CURRENT (µA) ALERTACC vs. Fan Speed vs. Temperature 13000 12000 TA = -40˚C 11000 10000 9000 8000 7000 6000 5000 4000 3000 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 TA = +25˚C 100 95 90 85 80 75 70 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 5.7 6.0 FAN SPEED (RPM) TA = +90˚C VDD = 3.0V 2.0 4.0 6.0 8.0 10.0 ALERTACC (%) SUPPLY VOLTAGE (V) THRESHOLD Voltage vs. Fan Speed vs. Supply Voltage (VDD) 15000 14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 0.00 0.25 VDD = 3.6V Alert Output Delay (TDELAY) vs. Power Supply Voltage (VDD) ALERT OUTPUT DELAY TIME (ms) 177 176 175 174 173 172 171 170 169 168 2.5 3.0 3.5 4.0 4.5 5.0 POWER SUPPLY VOLTAGE (VDD) VDD = 3.3V VDD = 3.0V VDD = 2.7V VDD = 5.5V FAN SPEED (RPM) VDD = 5.0V 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 THRESHOLD VOLTAGE (V) ALERT VLOW vs. ALERT ISINK 160 ALERT VOUT LOW (mV) CLEAR Pin HIGH to ALERT pin HIGH Timing Diagram 140 120 100 80 60 40 20 0 0.5 1 1.5 2 2.5 VDD = 2.7V VDD = 5.0V VDD = 3.6V VDD = 3.0V VDD = 5.5V 3 3.5 4 4.5 ALERT ISINK (mA) © DS21688B-page 4 2002 Microchip Technology Inc. TC670 4.0 DETAILED DESCRIPTION FIGURE 4-2: VDD = +5V 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. TYPICAL APPLICATION CIRCUIT 4V DD 0.1 µ F 3 From R3 Microcontroller CLEAR ALERT 1 R2 5 ALERT LED FIGURE 4-1: TC670 BLOCK DIAGRAM R4 +12V VDD CLEAR THRESHOLD Logic ALERT Vthreshold THRESHOLD 6 SENSE GND 2 CSENSE DC FAN RSENSE SENSE GND Frequency to Voltage Bandgap Oscillator 50kΩ 124mV V THRESHO LD =V Note: This typical application circuit uses an LED to indicate that a fan failure has occurred. 4.1 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 a DC voltage present on the THRESHOLD pin. If the converted frequency-to-voltage value from the fan’s pulses falls below the THRESHOLD voltage, a FAULT signal is asserted through the ALERT pin (active LOW). In a 3.0V system, the external fan alert level on the THRESHOLD pin can be designed from 0.0V (stalled fan) and up to 2.4V (for 13,000 RPM) to cover most of the common fan speeds. This failure detection system works with linear controlled 2-wire fans and eliminates the need for 3-wire fans. The TC670 can work with 3wire fans as well 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 output 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. SENSE Input As shown in Figure 4-2, the SENSE input (Pin 6) is connected through a sensing capacitor (CSENSE). A low value current sensing resistor (RSENSE) is also connected to the low side of the fan to the ground return leg of the fan. 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. 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 across the sense capacitor. The current across CSENSE is terminated with the internal 50kΩ input resistance at the SENSE pin of the TC670. When positive going fan pulses at the SENSE input are greater than 124mV (typ) the TC670 latches in those voltage spikes. This 124mV (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. 2002 Microchip Technology Inc. DS21688B-page 5    R2 --------------------DD R + R 2 3    © TC670 The design of the proper input SENSE circuitry is a matter of scaling RSENSE to provide the necessary amount of gain and proper selection of the sensing capacitor. The following table (Table 4-1) lists some recommended values for RSENSE according to the nominal operating current of the fan. Please note that the current draw specified by the fan manufacturer may not be the fan’s nominal operating current, but a worstcase rating. If the fan current falls between two of the values listed, it is recommended that the higher value resistor is used. 4.2.1 THRESHOLD CALIBRATION USING FAN’S FULL SCALE SPEED The fan should first be run at full speed. At full speed the THRESHOLD voltage level should be adjusted until the ALERT output is asserted. With this full scale value of the THRESHOLD voltage, the value can be scaled down to the Fan Fault speed as a percentage of the full speed. For example, if the fan full speed THRESHOLD voltage is 1.5V, then the Fan Fault THRESHOLD voltage at 30% of full speed would be 30% x 1.5V = 0.45V. TABLE 4-1: RECOMMENDED VALUES FOR RSENSE PER FIGURE 4-2 RSENSE (Ω) 4.7 2.4 1.8 1.3 1.0 0.8 4.2.2 Nominal Fan Current (mA) 100 200 300 400 500 600 THRESHOLD CALIBRATION USING FAN’S MINIMUM ALLOWABLE SPEED ESTIMATE For a more exact Fan Fault trip point, the user can run the fan at its minimum allowed speed. At this speed, the THRESHOLD voltage can be adjusted until the ALERT output is asserted. 4.3 CLEAR Input A 0.1µF ceramic capacitor is recommended for CSENSE. Smaller capacitor values will require larger sense resistors whereas larger capacitors are more expensive and occupy more board space. The CLEAR input allows the user to reset the ALERT pin to a high status. This is an active HIGH input. Consequently, as long as CLEAR is HIGH, ALERT will always be HIGH as well. To allow ALERT to operate correctly CLEAR must be held LOW. This feature can be implemented so that false Fan Fault conditions do not initiate system shutdown. 4.2 THRESHOLD Input 4.4 ALERT Output The voltage at the THRESHOLD input sets the equivalent minimum allowable fan speed for the application. As shown in Section 3.0 typical performance curves, the relationship between the THRESHOLD voltage and minimum fan speed is also power supply and temperature dependant. All the values for the THRESHOLD voltage that are shown in these graphs represent typical numbers and might not be optimized for all fans in all applications. To ensure accurate fan speed monitoring of a specific fan in a specific application, the user must perform a onetime correlation check with the prototype. There are two techniques that can be used to calibrate the system. One approach is to find the fan’s full scale capability and mathematically estimate the minimum acceptable speed of the fan. A second technique is to identify the fan’s minimum speed and calibrate the THRESHOLD voltage accordingly. The ALERT output is an open drain output capable of sinking 2.5mA (typ). The ALERT output is asserted whenever the detected fan speed equals or falls below the equivalent voltage set at the THRESHOLD pin. The ALERT output is only deactivated once the CLEAR pin is brought to a HIGH state. Although the absolute maximum output current of this pin is 25mA, it is recommended that this current sinking into the ALERT Output does not exceed 20mA. 4.5 Power Supply Input, VDD To assure proper operation of the TC670 in a noisy environment where the fans are running, the V DD pin (Pin 4) must be decoupled with a 0.1µF capacitor as shown in Figure 4-1. This capacitor should be located as close to the TC670 V DD pin as possible as well being promptly terminated to the ground plane. A Ceramic capacitor is recommended. 4.6 Ground Terminal, GND The GND pin (Pin 2) of the TC670 should be connected directly to the analog ground plane of the circuit board. Care should be taken in circuit layout to keep this pin away from switching signals, such as the fan excitation signals in order to avoid false signals on the SENSE pin. © DS21688B-page 6 2002 Microchip Technology Inc. TC670 5.0 5.1 PACKAGE INFORMATION Package Marking Information 6-Pin SOT-23A (EIAJ SC-74) Device 3 2 1 4 5 6 1 & 2 = part number code + temperature range and voltage Part Number TC670ECH 3 = year and quarter code 4 = lot ID number Code 2002 Microchip Technology Inc. DS21688B-page 7 © TC670 5.2 Taping Form Component Taping Orientation for 6-Pin SOT-23A (EIAJ SC-74) Devices User Direction of Feed Device Device Device Device Device Device Marking Marking Marking Marking Marking Marking W PIN 1 P Standard Reel Component Orientation For TR Suffix Device (Mark Right Side Up) Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size 6-Pin SOT-23A 8 mm 4 mm 3000 7 in 5.3 Package Dimensions SOT-23A-6 .075 (1.90) REF. .122 (3.10) .098 (2.50) .020 (0.50) .014 (0.35) .069 (1.75) .059 (1.50) .037 (0.95) REF. .118 (3.00) .110 (2.80) .057 (1.45) .035 (0.90) .006 (0.15) .000 (0.00) 10° MAX. .024 (0.60) .004 (0.10) .008 (0.20) .004 (0.09) Dimensions: inches (mm) © DS21688B-page 8 2002 Microchip Technology Inc. TC670 SALES AND SUPPORT Data Sheets Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following: 1. 2. 3. Your local Microchip sales office The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277 The Microchip Worldwide Site (www.microchip.com) Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using. New Customer Notification System Register on our web site (www.microchip.com/cn) to receive the most current information on our products. 2002 Microchip Technology Inc. DS21688B-page 9 © TC670 NOTES: © DS21688B-page 10 2002 Microchip Technology Inc. TC670 Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip’s products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights. 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