Abstract: The TC652 and TC653-type-specific integrated circuit testing microprocessor chips and microprocessor cooling temperature protection circuit design, thus ensuring long-term safe and reliable micro-processing work.
  Keywords: Microprocessor integrated temperature sensor detects thermal protection circuit
  U.S. Telcom TC652 and TC653 ASIC company. It is by detecting the computer system microprocessor (µP) temperature, brushless DC fan speed control to improve the µP thermal conditions to ensure safe and reliable long-term µP work. TC652 and TC653 can be used in PC and notebook computers in the thermal protection circuit, but also for set-top boxes (Set-Top Box), digital communication equipment, computer peripherals, instrumentation and monitoring systems. The difference is the increase in the automatic off mode TC653, below the lower limit temperature can be automatically shut down the fan, to save power.

1 TC652/653 performance characteristics and working principle
  1.1 Features
  (1) TC652/653 contain integrated temperature sensor and A / D converter is a µP can simultaneously detect the temperature and fan operation temperature control of the situation-specific IC.
  (2) The temperature range is -40 ~ +125 ?. In the range of +25 ~ +70 ? temperature accuracy of ± 1% (typical value).
  (3) using pulse width modulation (PWM) mode, the speed controller using a hierarchical multi-level speed of the fan. ?P output pulse duty cycle is proportional to the temperature. Using the above control can not only extend the life of the fan to save energy, can reduce fan noise.
  (4) All procedures have been solidified in the chip, not the top software support, are not subject to computer control. Temperature range (ie maximum temperature, minimum temperature tH tL with interval) according to the model number suffix may be, there are 10 kinds of specifications.

(5) Power supply voltage range (+28 ~ +5.5 V), low power consumption (quiescent current of only 50µA).
1.2 Work
TC652/653 internal block diagram shown in Figure 1. They are 8-pin MSOP package. UDD, GND, respectively, for the positive supply-side and public places. FAULT output of the fan failure alarm, low output indicates that the fan is faulty. A failure, TC652/653 locked in the off mode, PWM output remains low. If SHDN high or on the termination power to the UDD again, you can make the chip and fan from the off state to return to normal operation. SHDN input control the fan is off, input is low, forcing the fan off. During the off mode, TC652/653 able to monitor the µP's temperature, if t> tH, Tover end to the output low. SENSE fan for the detection of the input pulse can be detected through a resistor Rs to the fan pulses. If not detected pulse signal, it means that the fan is defective. Tover for the over-temperature alarm terminal. When the temperature exceeds tH µP, the end of the output low. PWM for the fan drive pulse output, pulse width modulation frequency of approximately 15Hz.
TC652/653 including the internal temperature sensor, A / D converter, oscillator, temperature setting and fine-tuning circuit, the logic control circuit duty cycle, output level, comparator, and the fan detection logic circuit. Temperature signal after A / D converted into temperature data, stored in the internal register. The register has a pre-defined threshold temperature, there are six initial temperature (tL, t1, t2, t3, t4, tH), t1 ~ t4 is evenly distributed under the control of the temperature range (tL ~ tH) in Table 1. Where, t
Table 1 TC652/653 defined temperature range and the output duty cycle
Temperature tt
Duty DTC65240% 50% 60% 70% 80% 90% 100% 100% and over-temperature alarm (Tover = 0)
TC653 "OFF" (auto-off mode) 50% 60% 70% 80% 90% 100%
TC652/653 the basic working principle is to use the temperature data detected by the µP, changing the duty cycle of PWM output signal, and through external power switch to control the DC fan speed, thereby improving the thermal conditions of µP. TC652 duty cycle adjustment range of 40% ~ 100%, TC653 and 50% to 100%. To ensure the reliability of the fan, at the beginning or from a power down mode to restart the chip, triggering the timer so that the PWM output at high for 2 seconds, Off mode timing waveforms shown in Figure 2 . Fan fails in the confirmation to the internal circuit through the PWM, FAULT side have become low.

Tover signal with a temperature hysteresis. When t> tH +10 ? when, Tover only become low end, said µP overheat, turn off, µP power supply, also make the system work in the full state of the other fans, further cooling to the µP; when t
  2 microprocessor thermal protection circuit
  Typical Application Circuit 2.1 TC652/653
  TC652/653 typical application circuit shown in Figure 3. TC652/653 be detected close to the microprocessor (µP), and by its fan failure alarm signal sent FAULT, sent to the computer system fan failure alarm input, after the computer receives the signal from the console to turn off TC652/653 send a shutdown signal SHDN, turn off PWM output. When the µP's temperature exceeds the set limit temperature tH, from Tover ended output over temperature alarm signal is also sent to the computer system. TC652/653 with +5 V power supply, +12 V power supply fan alone. VT external drive tube type 2N2222 NPN transistor with its main parameters are: U (BR) CEO = 30V, Ic = 150mA, ICM-800mA, Pcm = 500mW, hFE = 50. RB-based limit resistor, Rs is the resistance of the fan pulse detection. Capacitor C is used to filter out high frequency noise.
  2.2 The design issues
  2.2.1 driver the choice of tube parameters and typical products
  According to the fan running at full speed when the current IFAN value, to determine the type of driver control. In principle, when the IFAN = 300mA, the optional bipolar transistor or FET; when IFAN> 300mA, you must use N-channel MOSFET. Typical products bipolar transistor MPS2222, 2N4410 and MPS6602. N-channel MOSFET Typical products Si2302, MPS6602, and BS170.
  2.2.2 base the calculation of the limit current resistor RB
  Drive the fan using a bipolar transistor, the base resistor RB limit value is determined by:
  RB = [UON-UBE (SAT)-URS] / IBM
  Where, UOH - PWM high-side output voltage;
  UBE (SAT) - the base - emitter saturation voltage;
  URs - the fan current sense resistor voltage drop on Rs;
  IB - base current.
  For example: Known UOH = 4.0V, VBE (SAT) = 1.3V, VRs = IFAN · Rs = 150mA × 3.0O = 0.45V, IB = 3.25mA, can be obtained from the above equation RB = 1kO.

2.2.3 Current sense resistor Rs and fan relations IFAN
Current sense resistor Rs and fan correspondence between IFAN Table 2.
Table 2, the fan current sense resistor Rs and the corresponding relationship between IFAN
IFAN/mA50100150200250300350400450500
Rs/O9.14.73.02.42.01.81.51.31.21.0
2.2.4 The method of reducing fan noise
When the fan runs at full speed airflow disturbance formed the main reason is to produce audio noise. Fan with fan speed controller allows the speed at less than full speed operation, which helps to reduce fan noise. In the regulation of the duty cycle of PWM signal, it can cause audio noise in the drive pipe parallel between the base and to a delay capacitor C can reduce the fan noise, the circuit shown in Figure 4a. And electric fan torque angle curve as shown in Figure 4b. Add delay capacitor, can be filtered out when the fan opening in the formation of PWM peak voltage, PWM signal smoothing role to play, so the fan torque change smoothly, thereby reducing the fan noise. Delay capacitor range 0.47 ~ 1.0µF. In addition, when the PWM = 0 to VT off, the delay capacitor can limit the increase of the reverse electromotive force of drive tube protective effect.