By Maxim Integrated 49
The Maxim MAX6655 and MAX6656 are precise voltage and temperature monitors. The digital thermometer reports the temperature of two remote sensors and its own die temperature. The remote sensors are diode-connected transistors, typically a low-cost, easily mounted 2N3906 PNP type, that replace conventional thermistors or thermocouples. Remote accuracy is ±1°C for multiple transistor manufacturers with no calibration necessary. The remote channels can also measure the die temperature of other ICs, such as microprocessors, that contain a substrate-connected PNP with their collector grounded and base and emitter available for temperature-sensing purposes. The temperature is digitized with 11-bit resolution.
The MAX6655 and MAX6656 also measure their own supply voltage and three external voltages with 8-bit resolution. Each voltage input's sensitivity is set to give approximately 3/4-scale output code when the input voltage is at its nominal value. The MAX6655 operates at +5 V supply and its second voltage monitor is 3.3 V. The MAX6656 operates on a +3.3 V supply and its second voltage monitor is 5 V.
The two-wire serial interface accepts standard SMBus™ Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read data. The MAX6655 and MAX6656 provide SMBus alert response and timeout functions. Additionally, the devices measure automatically and autonomously, with the conversion rate programmable. The adjustable rate allows the user to control the supply current.