Effective thermal management is important to the proper operation of many electronic systems today. Many microprocessors and integrated systems rely on built-in sensors to detect over or under-temperature situations and adjust their performance to ensure the system is operating in a safe state and ensure a long operational life. Other systems are specifically built to maintain environmental conditions and provide active control of the equipment around them.
Equipment huts for cellular base stations and remote radio units need to have environmental controls that prevent equipment from becoming too hot and either shutting down or experiencing a shortened lifespan. Extreme cold can also cause malfunctions, particularly during cold-start situations where equipment is resting unpowered at temperatures that are too cold for the proper operation of oscillators, microprocessors, and other critical system components. Environmental sensing and controls can help to ensure that an acceptable operating temperature is maintained regardless of the surrounding environment. The food service industry presents another critical application for temperature sensing and management systems as the operators of refrigeration systems for food storage, food prep areas, and other cold storage applications typically have safety related legal obligations to maintain carefully controlled cold environmental conditions.
An essential part of thermal management solutions is accurate temperature sensing. Algorithms can come close to predicting temperatures of a system based on weather data or other sources of temperature data, but complex interactions of variables such as solar loading on a partly cloudy day, unpredictable localized cooling, and variations in the efficiency of equipment performance over time make them an approximation at best. For this reason, many systems rely on sensors to measure the temperature of the environment around them to provide more accurate control of thermal management solutions. This can be particularly critical for food service and other industries that need to maintain strict environmental conditions to ensure the safety of food or to keep equipment operating at optimal temperatures. Temperature sensing can also be leveraged to enable alerts that signal when conditions have gone outside of limits and intervention is needed to maintain safety and restore systems to their proper operating conditions.
Introducing Microchip's MCP990X Temperature Sensors Series
In response to these needs, Microchip Technology has released their MCP990X series of 2-, 3-, and 4-channel, high accuracy, low cost SMBus temperature sensors. These chip sensors support contain an internal precision thermal diode and support up to three external sensors. The sensors are tuned specifically for low temperatures down to -40°C, with resolutions of 0.125°C. Typical accuracy for the internal temperature sensor is ±0.25°C from -40° to 65°C, and remote sensors have a ±1°C accuracy and extend the measurable range up to 105°C.
The MCP9902 is a 2-channel sensor in a tiny 2x2 WDFN package, while the MCP9903 and MCP9904 3-, and 4- channel sensors are packaged in a 3x3 WDFN. Temperature information is provided via a standard SMBus and I2C compatible interface to allow easy implementation in most monitoring systems without the need for a separate analog to digital converter. Two separate THERM# and ALERT# outputs are also provided to provide dedicated interrupts during temperature alerts. The THERM# output asserts when any of the measured temperatures exceed user programmed thresholds for a programmed number of consecutive measurements. Sensor indication is provided by varying the output voltage of the THERM# pin to indicate which combination of sensors are over their respective thresholds, and clears once all sensors fall beneath their programmed thresholds. The ALERT#/THERM2# output can be configured for a persistent ALERT output or to operate as a second THERM alert. Implementation of the MCP9902 is very simple, as only three active chips and a small number of passive components are required for an operational design.
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Features of Microchip's MCP990X Temperature Sensors Series
Several features in the MCP9002 series allow for excellent measurement accuracy and significant design flexibility. First, Resistance Error Correction (REC) provides automatic correction for up to 100 ohms of series resistance on external temperature sensor ports. Trace impedance, wiring series impedance, on die resistance, and bulk resistance in the base and emitter of a temperature transistor can all be corrected, allowing greater accuracy on the external power leads. For example, a remote temperature sensor can be placed hundreds of feet away from the MCP990X series device as long as the series impedance of the circuit and attached sensors stays below 100 ohms. Overall design flexibility is enhanced, as temperature sensors can be placed wherever they are needed, rather than being tied to the immediate proximity of the sensor system. It also allows diodes to be placed in a manner that isolates localized heat from the sensor and ensures the control system does not impact sensor measurements – essentially keeping the heat out of cold systems.参阅相关产品
Automatic Beta Compensation is another feature of the MCP990X series devices. This simplifies system design and setup by eliminating the need to provide unique sensor configurations for each application; optimum beta variation settings for the attached sensor are automatically applied for sensors attached to the first external sensor channel. In addition to automatically detecting the type of temperature sensor attached, this feature also corrects for beta variation in fine geometry processors. Supported sensor types include discrete temperature diodes as well as diodes integrated into microprocessors and other integrated circuits. For extreme situations with the most challenging sensor configurations, the external diode ideality factor can be programmed to correct for errors that cannot otherwise be corrected. This feature is not needed for the vast majority of designs, but it provides an additional option if a problematic implementation needs a bit of additional tweaking to achieve its intended function.
Integrating Microchip's MCP990X Devices
Microchip has provided several references to assist designers with the integration of the MCP990X devices into their designs. The MCP9902 product page contains an overview of the product as well as links to important references, including the MCP9902/3/4 Data Sheet. A USB powered evaluation board is also available, and contains a USB to I2C/SMBus bridge, demonstration circuit for the REC features of the part, several test points for ALERT#, THERM# and power, LED indicators for several functions, Remote diode interfaces, and other features that allow a complete evaluation of the parts. Several other resources are available online. A user guide contains detailed instructions on the use of the evaluation board, a YouTube video demonstration of the evaluation board visually guides designers through the evaluation of the device, and a recommended electronicdesign.com article lists several recommended remote temperature sensors.
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If your design requires a highly accurate temperature sensing solution, Microchip’s MCP990X series of multichannel diode sensing systems provides an inexpensive solution with industry standard interfaces and robust autoconfiguration features that make implementation a breeze.