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TC650ECVUA Folha de dados(PDF) 5 Page - Microchip Technology |
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TC650ECVUA Folha de dados(HTML) 5 Page - Microchip Technology |
5 / 14 page © 2002 Microchip Technology Inc. DS21450B-page 5 TC650/TC651 3.0 DETAILED DESCRIPTION The TC650/TC651 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 TC650/TC651 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 TC650/TC651 include an on-chip over-temperature alarm (TOVER) that gives a low signal when the temperature of the chip exceeds TH by 10°C, (typical). This feature eliminates the need for a separate temperature sensor for over-temperature monitoring. TABLE 3-1: TEMPERATURE RANGE DEFINITION FOR TC650 (MINIMUM-SPEED MODE) TABLE 3-2: TEMPERATURE RANGE DEFINITION FOR TC651 (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 TC650 and 50% to 100% for the TC651. 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 Over-Temperature Alert (TOVER) This pin goes low when the TH set point is exceeded by 10oC (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. 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% with Over-Temp Alert (TOVER =L) Note:The temperature regions defined by the six temperature thresh- olds are pre-defined in the TC650/TC651 by means of trimming. Once aTL and TH are programmed, the T1 –T4 thresholds are automatically equally spaced between TL and TH. Temperature Sensor Duty Cycle Logic Control A/D Converter Oscillator Temperature Set Point and Trim Range SHDN TOVER PWM VDD V+ |
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