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TC652CCVUA Datasheet(PDF) 5 Page - Microchip Technology |
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TC652CCVUA Datasheet(HTML) 5 Page - Microchip Technology |
5 / 14 page © 2002 Microchip Technology Inc. DS21453B-page 5 TC652/TC653 3.0 DETAILED DESCRIPTION The TC652/TC653 acquire and convert their junction temperature (TJ) information from an on-chip solid state sensor with a typical accuracy of ±1°C. The temperature data is digitally stored in an internal register. The register is compared with pre-defined threshold values. The six threshold values are equally distributed over a pre-defined range of temperatures (See Table 3-1 and Table 3-2). The TC652/TC653 control the speed of a DC brushless fan using a fractional speed control scheme. The output stage requires only a 2N2222-type small-signal BJT for fans up to 300mA. For larger current fans (up to 1 Amp) a logic-level N-channel MOSFET may be used. In addition to controlling the speed of the fan, the TC652/ TC653 include an on-chip over-temperature alarm (TOVER) that gives a low-true signal when the temperature of the chip exceeds TH by 10°C. This feature eliminates the need for a separate temperature sensor for over-temperature monitoring. In normal fan operation, a pulse-train is present at SENSE, Pin 5. A Missing Pulse Detector monitors this pin during fan operation (FanSense™ technology). A stalled, open, or unconnected fan causes the TC652/ TC653 to trigger its Start-up Timer once. If the FAULT persists, the FAULT output goes low, and the device is latched in its Shutdown mode. To release the fan from shutdown, toggle the SHDN or VDD pin. TABLE 3-1: TEMPERATURE RANGE DEFINITION FOR TC652 (MINIMUM-SPEED MODE) TABLE 3-2: TEMPERATURE RANGE DEFINITION FOR TC653 (AUTO-SHUTDOWN MODE) FIGURE 3-1: FUNCTIONAL BLOCK DIAGRAM 3.1 PWM Output The PWM pin is designed to drive a low cost transistor or MOSFET as the low side power switching element in the system. This output has an asymmetric complementary drive and is optimized for driving NPN transistors or N-channel MOSFETs. Since the system relies on PWM rather than linear power control, the dissipation in the power switch is kept to a minimum. Generally, very small devices (TO-92 or SOT packages) will suffice. The frequency of the PWM is about 15Hz. The PWM is also the time base for the Start-up Timer (see paragraphs below). The PWM duty cycle has a range of 40% to 100% for the TC652 and 50% to 100% for the TC653. Temperature (T = TJ) PWM Duty Cycle T< TL 40% TL<=T< T1 50% T1 <=T <T2 60% T2 <=T <T3 70% T3 <=T <T4 80% T4 <= T<TH 90% TH <= T<TOV 100% TOV < = T 100% with Over-Temp Alert (TOVER =L) Temperature (T = TJ) PWM Duty Cycle T< TL “OFF” TL<=T <T1 50% T1 <=T <T2 60% T2 <=T < T3 70% T3 <=T < T4 80% T4 < =T< TH 90% TH <=T<TOV 100% TOV <= T 100% withOver-Temp Alert (TOVER =L) Note: The temperature regions defined by the six tempera- ture thresholds are pre-defined in the TC650/651 by means of trimming. Once a TL and TH are programmed, the T1 -T4 thresholds are automatically equally spaced between TL and TH. Temp Sensor Fan Detect Logic Duty Cycle Logic Control AD Converter Oscillator Temperature Set Point and Trim Range SHDN TOVER PWM FAULT 90mV VDD V+ CMPTR + - 20k - - |
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