A temperature monitor capable of measuring three temperature zones
You may use an ADT7461 single channel temperature monitor, an ADG708 low voltage low leakage CMOS 8-to-1 multiplexer, and three standard 2N3906 PNP transistors to measure temperatures in three separate remote high temperature zones (Fig.1). Resistor R of MultiplexerONRelating to three transistors; Channel Matching and Resistor RONFlatness usually results in different temperature offsets. The ADT7461 temperature monitor used in this system can automatically cancel out the resistance in series with the external temperature sensor, so it can be used as a multi-channel temperature monitor. After the resistance is automatically cancelled, RONFlatness and changes between channels have little effect. Resistance associated with printed circuit boards and connectors will also be offset, allowing you to place the remote temperature sensor at a distance from ADT7461. This design does not require user calibration, so the ADT7461 can be directly connected to a multiplexer. ADT7461 Digital Temperature Monitor can measure the temperature of the external sensor, which is [+] 1]. The remote sensor may be a monolithic or discrete transistor, usually connected to the D+ and D-pins on the ADT7461. In addition to the remote sensor temperature channel, the ADT7461 has an on-chip sensor.
Three transistors connected to a diode whose emitters are connected together and then to the D+ input pin of ADT7461. Each base-collector junction with a separate multiplexer input pin (S)
1~ S
3) Connect. You can connect the selected remote transistor to the input pin D-, ADT7461, simply by addressing the multiplexer digitally controlled by addresses A, A1, and 20. The ADT7461 then measures the temperature of the connected transistor through a multiplexer. ADT7461 measures the temperature of the selected transistor without interference from other transistors. Figure 2 shows the temperature measurement results of three remote temperature sensors. The sensor temperature with address 000is room temperature. The temperature of the sensor with address 001 is low; The temperature of the sensor with address 010 is high. When you do not select an external sensor, the "open" flag in the ADT7461 register is activated to warn the interrupt output that there is signal output. You can extend the system to include as many external temperature sensors as you need for your design. One factor that limits the number of external sensors is the time used to measure all temperature sensors. If your design requires dual-line serial control of the multiplexer, you can use ADG728 instead of ADG708.
