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TC651ACV датащи(PDF) 7 Page - STMicroelectronics |
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TC651ACV датащи(HTML) 7 Page - STMicroelectronics |
7 / 16 page 2004 Microchip Technology Inc. DS21450C-page 7 TC650/TC651 4.0 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 tem- perature data is digitally stored in an internal register. The register is compared with pre-defined threshold val- ues. The six threshold values are equally distributed over a pre-defined range of temperatures (see Table 4- 1). The TC650/TC651 control the speed of a DC brush- less fan using a fractional speed-control scheme. The output stage requires only a 2N2222-type, small-signal BJT for fans up to 300 mA. 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 overtemperature alarm (TOVER) that gives a low signal when the temper- ature of the chip exceeds TH by 10°C (typical). This fea- ture eliminates the need for a separate temperature sensor for overtemperature monitoring. Figure 4-1 shows the block diagram of the device. FIGURE 4-1: Functional Block Diagram. 4.1 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 15 Hz. The PWM is also the time base for the Start-up Timer (see Section 4.2 “Start-Up Timer”). The PWM duty cycle has a range of 40% to 100% for the TC650 and 50% to 100% for the TC651. 4.2 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. 4.3 Overtemperature Alert (TOVER) This pin goes low when the TH set point is exceeded by 10°C (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 air- flow obstruction). This output may be treated as a “System Overheat” warning and be used to either trigger system shutdown or bring other fans in the system to full speed. The fan will continue to run at full speed while TOVER is asserted. Built-in hysteresis prevents TOVER from “chattering” when the measured temperature is at or near the TH + 10°C trip point. As temperature falls through the TH + 10°C trip point, hys- teresis maintains the TOVER output low until the measured temperature is 5°C above the trip point setting. 4.4 Shutdown (SHDN) The fan can be unconditionally shut down by pulling the SHDN pin low. During shutdown, the PWM output is low; ideal for notebook computers and other portable applications where you need to change batteries and must not have the fan running at that time. Thermal monitoring and TOVER are still in operation during shutdown. IDD shutdown current is around 50 µA. 4.5 Auto-shutdown Mode The TC651 features auto-shutdown. When the temperature is below the factory set point at minimum speed (TL), PWM is low and the fan is automatically shut off (Auto-shutdown mode). This feature is ideal for notebook computers and other portable equipment that need to conserve as much battery power as possible and, thus, run a fan when it is only absolutely needed. The TC651 will continue to be active in order to monitor temperature for TOVER. The TC651 exits Auto- shutdown mode when the temperature rises above the factory set point (T1). Temperature Sensor Duty Cycle Logic Control A/D Converter Oscillator Temperature Set Point and Trim Range SHDN TOVER PWM VDD V+ |
Аналогичный номер детали - TC651ACV |
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Аналогичное описание - TC651ACV |
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