The MAX1618 precise digital thermometer reports the temperature of a remote sensor. The remote sensor is a diode-connected transistor - typically a low-cost, easily mounted 2N3904 NPN type - that replaces conventional thermistors or thermocouples. Remote accuracy is +-3C for multiple transistor manufacturers, with no calibration needed. The MAX1618 can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor. The 2-wire serial interface accepts standard System Management Bus (SMBus) Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read temperature data. The data format is 7 bits plus sign, with each bit corresponding to 1C, in two's complement format. Measurements can be done automatically and autonomously, with the 16Hz conversion rate or programmed to operate in a single-shot mode. The thermostat mode configures the ALERT output as an interrupt or as a temperature reset that remains active only while the temperature is above the maximum temperature limit or below the minimum temperature limit. The ALERT output polarity in thermostat mode can be configured for active high or active low. Fan control is implemented using this ALERT output. The MAX1618 is available in a small (1.1mm high) 10-pin uMAX package.