TC642DEMO FAN CONTROL MODULE FOR TC642/646 FEATURES GENERAL DESCRIPTION BOARD SCHEMATIC

Transcription

1 FAN CONTROL MODULE FOR TC642/646 FEATURES Complete Implementation of TC642 or TC646 Fan Control Circuitry on a 1.5" x 2.0" Board Works with Standard Thermistors Temperature-proportional Fan Speed Control Open Fan Stator/Blocked Rotor Detection Over Temperature Fault Detection Installs Directly in User's End Equipment Speeds Up Prototyping, System Development and System Thermal Characterization GENERAL DESCRIPTION The Fan Control Module is a blank circuit board that allows the user to quickly prototype fan control circuits based on Microchip s TC642 or TC646 PWM Fan Control ICs. It measures only 1.5 inches x 2.0 inches, allowing installation in the user s end equipment for system evaluation. It uses through-hole components for easy user assembly and evaluation. Versatile sensor input and output driver circuitry allows the Fan Control Module to be used with virtually any brushless DC fan and standard thermistor. An optional L.E.D. status indicator gives a visual indication of a fan fault condition (open stator, blocked rotor or over temperature fault detection). NOTE: An Excel-based spreadsheet is included with the TC642EV that is helpful in designing the thermistor network for the TC64x fan controllers. THMST.XLS is compatible with Office 95, while THMSTR7.XLS is compatible with Office 97. This utility also is available for downloading from the Microchip web site at: BOARD SCHEMATIC OPTIONAL INPUT R1 R2 C2 0.01µF Test Point (Typical) 1 V IN 8 6 C1 10µF C8 0.01µF R7 1.2k Q4 2N3906 R8 470 LED V OUT R3 R4 C3 0.01µF 3 2 C4 C F TC642 TC646 U1 4 V OUT SENSE 7 5 C6 0.1µF 0.47µF 1µF (Optional) Figure /16/97

2 BOARD ASSEMBLY The schematic for the Fan Control Module appears in Figure 1 (previous page), while Table 1 lists typical component values. Please refer to the Applications Section of the TC642 and TC646 data sheets for detailed usage information. Table 1. Fan Control Module Component List Component Typical Value Comments C1 10µF Radial Electrolytic Capacitor Power supply filter C2 0.01µF Ceramic Disk Capacitor Bypass capacitor C3 0.01µF Ceramic Disk Capacitor Bypass capacitor C4 0.47µF to 1.0µF Tantalum Capacitor PWM capacitor. Typical values are 1.0µF to 0.47µF (PWM frequencies of 30Hz to 60Hz). See TC642/646 data sheets. C5 Not Used C6 0.1µF Ceramic Disk Capacitor SENSE input coupling capacitor. 0.47µF to 1µF Radial Electrolytic Capacitor Fan acoustic noise suppression capacitor. (Optional) C8 0.01µF Ceramic Disk Capacitor Bypass capacitor L.E.D. 10mA Miniature L.E.D. L.E.D. lights when output is LOW (active). (Optional), 2N2222A NPN Transistor Darlington pair output option. If used, location MUST be left open. (See Applications section of TC642/646 data sheets). Single transistor output option. Can be bipolar transistor, or logic level MOSFET (depending on cost constraints and fan current). If used, and locations MUST be left open. Q4 2N3906 (or Equiv) PNP Transistor L.E.D. Driver transistor. (Optional) R1, R2 (See Applications section of TC642/646 data sheets). Value depends on type of sensor used, and desired fan speed vs. temperature profile. R3, R4 (See Applications section of TC642/646 data sheets). Value depends on desired minimum fan speed setting (TC642) or auto-shutdown temperature (TC646). (See Applications section of TC642/646 data sheets). Base current limiting resistor. Value depends on type of fan and driver used. Typical values appear in Table 2. (See Applications section of TC642/646 data sheets). Fan current sensing resistor. Value depends on full speed fan current. Typical values appear in Table 2. R7 1.2K, 1/4 Watt, 5% Resistor L.E.D. Drive transistor base resistor. (Optional) R8 470Ω 1/4 Watt, 5% Resistor L.E.D. Drive transistor series limiting resistor. (Optional) U1 TC642 or TC646 Fan Control I.C /16/97 2

3 C1 + C2 R3 R1 R4 R2 R7 Q4 FAN( ) + C8 C4 C3 U1 C6 C5 R8 + LED Additional pads in series with I.C. pins and board input connections 6-32 Drill (4) Figure 2. Fan Module Board Layout TYPICAL MODULE CONFIGURATIONS Using Bipolar Driver Transistors All component selections should be made based on information in the Applications section of the TC642 and TC646 data sheets. Table 2 is provided as a guide only, and lists typical Fan Module operating configurations for 12V fan applications. The values in the table assume the use of low cost, bipolar transistors (such as 2N2222A), unless stated otherwise. Table 2. Suggested Output Driver/Current Sense Values vs. Fan Motor Current Full Speed Darlington Single Fan Motor Pair Transistor Current (, ) () (Ω) (Ω) 50mA X 2.4K mA X 1.1K mA X mA X mA X 5.6K mA X 4.7K mA X 3.9K mA X 3.3K mA X 3.0K mA X 2.4K 1.2 Fan motors of 50mA to 150mA can be driven using the single transistor driver configuration (i.e., installed; and not installed). Fans having a motor current of 200mA may be driven using either the single transistor or Darlington configurations. If a single transistor is used, care must be taken to select a transistor having a guaranteed minimum h FE of at least 50 to ensure the maximum output current specification (5mA) of the TC642/646 is not exceeded. Using Logic Level MOSFETS Substituting a logic level MOSFET (such as a BS170) for results in lower system voltage losses and significantly reduces output loading on the TC642/646. The low R DSON of the MOSFET (1Ω in the case of the BS170) enables it to be used instead of the Darlington in high current fan applications (please see the TC642/646 data sheet Applications section for details). Population options for single transistor output drivers (using either MOSFET or bipolar transistor) and the two transistor (Darlington) stage is shown in Figure /16/97

4 C B E D G S C B E C B E REVERSE ORIENTATION OF AND JUMPER 7 TO FAN ( ) Jumper TO FAN ( ) (2N2222A) 7 (BS170) 7 TO FAN ( ) Figure 3. Output Driver Population Options, = 2N2222A SYSTEM CONNECTION FOR +5V OPERATION Figure 4 shows typical wiring connections to the Fan Control Module. The fan operating voltage is +12V while the Fan Control Module operates from a supply voltage of +5V. An NTC thermistor connects from the input of the Fan Control Module to as shown. Fan Control Module resistors R1 and R2 (Figure 1), and the characteristics of the NTC together determine the fan speed versus temperature profile of the system. SYSTEM CONNECTION FOR OPERATION FROM +12V AND 5V SUPPLIES The voltage losses in the system (i.e. output transistor V CESAT plus the IR drop across the current sampling resistor) may require operating the fan from a voltage greater than +12V. This is especially true when driving larger (i.e. >200mA) fans. Figure 5 shows operation from 17V using +12V and 5V supplies. The Fan Control Module line is referenced to 5V while the line is connected to ground. While the net voltage across the TC642/646 is therefore +5V. The low side of the output driver pulls to 5V +5V +12V NTC Thermistor System Shutdown FAN( ) FAN CONTROL MODULE POWER SUPPLY FAN Figure 4. Typical Wiring Connections to Fan Module for 12V fan and 5V Module Supply -02 9/16/97 4

5 during the active portion of the PWM cycle. The high side of the fan connects to +12V as usual. Care must be taken to level shift the signal from levels of ground and 5V to TTL-compatible signal levels. The level shifting is provided by R1, R2, R3 and D1 in Figure V NTC Thermistor FAN( ) FAN CONTROL MODULE 5V POWER SUPPLY +5V FAN R1 7.5k R2 7.5k D1 1N4148 R3 10k System Shutdown Figure 5. Typical Wiring Connections to Fan Module Operation from +12V and 5V Supply 5 Printed in the U.S.A /16/97

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