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TMP411 Datasheet(PDF) 20 Page - Burr-Brown (TI) |
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TMP411 Datasheet(HTML) 20 Page - Burr-Brown (TI) |
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20 / 25 page  TMP411 SBOS383A − FEBRUARY 2007 www.ti.com 20 SMBUS ALERT FUNCTION The TMP411 supports the SMBus Alert function. When pin 6 is configured as an alert output, the ALERT pin of the TMP411 may be connected as an SMBus Alert signal. When a master detects an alert condition on the ALERT line, the master sends an SMBus Alert command (00011001) on the bus. If the ALERT pin of the TMP411 is active, the devices will acknowledge the SMBus Alert command and respond by returning its slave address on the SDA line. The eighth bit (LSB) of the slave address byte indicates whether the temperature exceeding one of the temperature high limit settings or falling below one of the temperature low limit settings caused the alert condition. This bit will be high if the temperature is greater than or equal to one of the temperature high limit settings; this bit will be low if the temperature is less than one of the temperature low limit settings. See Figure 16 for details of this sequence. If multiple devices on the bus respond to the SMBus Alert command, arbitration during the slave address portion of the SMBus Alert command determines which device will clear its alert status. If the TMP411 wins the arbitration, its ALERT pin becomes inactive at the completion of the SMBus Alert command. If the TMP411 loses the arbitration, the ALERT pin remains active. SHUTDOWN MODE (SD) The TMP411 Shutdown Mode allows the user to save maximum power by shutting down all device circuitry other than the serial interface, reducing current consumption to typically less than 3 µA; see typical characteristic curve Shutdown Quiescent Current vs Supply Voltage. Shutdown Mode is enabled when the SD bit of the Configuration Register is high; the device shuts down once the current conversion is completed. When SD is low, the device maintains a continuous conversion state. SENSOR FAULT The TMP411 will sense a fault at the D+ input resulting from incorrect diode connection or an open circuit. The detection circuitry consists of a voltage comparator that trips when the voltage at D+ exceeds (V+) − 0.6V (typical). The comparator output is continuously checked during a conversion. If a fault is detected, the last valid measured temperature is used for the temperature measurement result, the OPEN bit (Status Register, bit 2) is set high, and, if the alert function is enabled, ALERT asserts low. When not using the remote sensor with the TMP411, the D+ and D− inputs must be connected together to prevent meaningless fault warnings. UNDER-VOLTAGE LOCKOUT The TMP411 senses when the power-supply voltage has reached a minimum voltage level for the ADC converter to function. The detection circuitry consists of a voltage comparator that enables the ADC converter after the power supply (V+) exceeds 2.45V (typical). The comparator output is continuously checked during a conversion. The TMP411 will not perform a temperature conversion if the power supply is not valid. The last valid measured temperature is used for the temperature measurement result. GENERAL CALL RESET The TMP411 supports reset via the Two-Wire General Call address 00h (0000 0000b). The TMP411 acknowledges the General Call address and responds to the second byte. If the second byte is 06h (0000 0110b), the TMP411 executes a software reset. This software reset restores the power-on reset state to all TMP411 registers, aborts any conversion in progress, and clears the ALERT and THERM pins. The TMP411 takes no action in response to other values in the second byte. IDENTIFICATION REGISTERS The TMP411 allows for the Two-Wire bus controller to query the device for manufacturer and device IDs to allow for software identification of the device at the particular Two-Wire bus address. The manufacturer ID is obtained by reading from pointer address FEh. The device ID is obtained by reading from pointer address FFh. The TMP411 returns 55h for the manufacturer code and 11h for the device ID. These registers are read-only. FILTERING Remote junction temperature sensors are usually implemented in a noisy environment. Noise is most often created by fast digital signals, and it can corrupt measurements. The TMP411 has a built-in 65kHz filter on the inputs of D+ and D− to minimize the effects of noise. However, a bypass capacitor placed differentially across the inputs of the remote temperature sensor is recommended to make the application more robust against unwanted coupled signals. The value of the capacitor should be between 100pF and 1nF. Some applications attain better overall accuracy with additional series resistance; however, this increased accuracy is setup-specific. When series resistance is added, the value should not be greater than 3k Ω. |
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