Abstract: The high-precision, 12-bit signal output from IC LM76 digital temperature sensor and two-temperature window comparator formed, it has low power consumption, wide range, serial bus interface and so on. This paper describes the operating characteristics of the circuit, pin functions and working principle of the LM76 is given for the API design of the typical application circuit.
  Keywords: digital temperature sensor alarm programmable window comparator gauge LM76
  1 Overview
  LM76 is a digital temperature sensor, I2C serial bus interface, the composition and temperature window comparator IC. At 70 ~ 100 and -10 ~ +45 temperature range,
The window comparator accuracy of the serial bus interface ± 1. At 25, LM76CHM accuracy up to ± 0.5 . It's open-drain interrupt output (INT) at temperatures in excess of programmable temperature window is activated, the temperature limit alarm output (T-CRIT-A) in the risk of extreme temperature exceeds a programmable temperature (over this temperature will damage the LM76) valid.
  LM76 host can control the window, the lower temperature limits and dangerous program, its failure queue with programmable hysteresis can minimize false positives. LM76 power on the system after the first threshold value in a default state. The default threshold of its sensors: Hysteresis temperature THYST = 2 ,
Minimum temperature TLOW = 10 , maximum temperature, THIGH = 64 , dangerous temperature extremes TCRIT = 80 .
  LM76 3.5V and 5V power supply used, and has a serial bus interface, using 12-bit signal output, the maximum measurement range of more than 127 , LM76, these features make it can be widely used for temperature control systems, protection of personal computers, electronic test equipment , office equipment and biomedical instruments and so on.
  LM76 has the following characteristics:
  Window comparator simplifies the design of ACPI, also compatible temperature monitoring and control;
  with a serial bus interface;
  The open-drain interrupt output isolation and the temperature gauge turned off;
  shutdown mode with minimal power consumption;

a bus can be connected to more than 4 LM76 chip;
  12-bit signal output with a maximum range 127 .
  2 LM76 pin function and the main parameters
  LM76 pinout shown in Figure 1, the function of each pin listed in Table 1.
  Pin description Table 1 LM76
  Symbol Pin features a typical connection
  SDA1 serial bidirectional data lines, open drain output, CMOS logic level pull-up resistor, the controller's I2C data line
  SCL2 serial bus clock input, CMOS logic level access control of the I2C clock line
  T-CRIT-A3 temperature limit alarm, open drain output connected to the resistor, the controller or the system hardware broken off in the end
  GND4 grounded power
  INT5 interruption, open-drain output pull-up resistor connected to the controller's interrupt line
  + Vs8 positive supply voltage 3.3V or 5V power input termination
  A0 ~ A17, 6 to set the address of the user input is grounded (low, "0") or access + Vs (high, "1")
  LM76 main parameters are as follows:
Supply voltage: 3.3V or 5V;
  Supply Current: Working state is 250µA (typical), 450µA (max); off when 8µA (max);
Measurement Accuracy: ± 0.5 (25 when the maximum); -10 ~ +45 when ± 1.0 (maximum);
  Resolution: 0.0625

3 LM76 internal structure of the
  Figure 2 shows the IC LM76 precision temperature diagram of the internal structure can be seen, LM76 temperature sensor includes a bandgap temperature sensor, a 13-bit ADC and a user-set upper and lower limits of the digital comparator . When the temperature outside the window in TLOW and THIGH, the comparator activates INT line; when the temperature exceeds TCRIT, the comparator activates T-CRIT-A line. These lines of work mode and polarity are programmable.
  LM76 as a slave device on the serial bus running, SCL line is the input line, SDA line is bi-directional serial data line. According to the serial bus specification, LM76 has a 7-bit slave address, controlled address the most significant bit set to "10010", the other two pins assigned to the least significant bits A0, A1, and through the A0, A1, or ground then + Vs to set "0" or set to "1." The complete slave address is:
  10010A1A0
  ASB LSB
  4 Application examples
  ACPI Figure 3 is designed to meet the requirements of a typical application circuit. Which, LM76 temperature window for the selected program, and when the temperature exceeds the window limit,
LM76 will interrupt signals the microprocessor, its identification can quickly determine the internal temperature is up or down. When the temperature exceeds the limit temperature TCRIT time, LM76 off by the hardware and the micro processing circuit disconnected. INT output and T-CRIT-A output is separated from each other, but can be through the line - or together. In addition, T-CRIT-A diodes, or door can be connected to the INT line, in this way can the process of T-CRIT-A activates INT line, but the process can not activate INT T-CRIT-A line, which at the same time to the microprocessor device and the LM76's T-CRIT-A closed circuit the process of the report is very useful.
  Figure 4 shows the ACPI specification and the corresponding temperature alarm shut down the system. The circuit through the power of the auxiliary output to start the LM76, and then to close failures or overheating of the computer system to protect as much as possible.