System temperature monitoring method analysis
Published time: 2019-07-17
For many system designs, it is necessary to monitor high power components (processors, field programmable gate arrays, field effect transistors) to ensure system and user safety. The accuracy of temperature readings is important because it allows designers to maintain performance while maintaining safety limits or to reduce system cost by avoiding over-engineering elsewhere. Texas Instruments' family of compact, high-precision temperature sensors can be placed closer to these critical components for the most accurate measurements.
How to monitor board temperature
Temperature problems in the circuit can affect system performance and damage expensive components. By measuring the temperature of an area of a printed circuit board (PCB) where hot spots or high-power integrated circuits (ICs) are present, it helps to identify thermal issues and take preventive or corrective action in a timely manner.
You may want to monitor the die temperature of a high-power IC (such as a central processing unit, dedicated IC, field programmable gate array, or digital signal processor) to dynamically adjust its performance, or you may want to monitor the hot zone around the power stage so that Control the fan speed in the system or initiate a safety system shutdown procedure. The ultimate goal is to optimize performance and protect expensive equipment.
Heat transfer from PCB to temperature sensor
Local temperature sensors measure their own die temperature to determine the temperature of a particular area. Therefore, it is important to understand the main temperature conduction path between the die and the object or environment surrounding the sensor. Thermal conduction is primarily through two paths: by connecting to the packaged die attach pad (DAP) or by packaging the lead pins. DAP, if present, provides the most important thermal path between the PCB and the die.
If the package type does not contain DAP, the leads and pins provide the most important thermal path.
The molding compound provides an additional thermally conductive path, but due to its low thermal conductivity, any heat transfer by the molding compound itself is slower than heat transfer by the lead or DAP.
The package type determines how quickly the temperature sensor responds to temperature changes. The figure below shows the relative thermal response rates for different types of selected surface mount technology package types for temperature measurement.
Packages without molding compounds (chip scale package, die size ball grid array package) and packages with DAP (quad flat no-lead [QFN] package, bilateral flat leadless [DFN] package) are designed for PCBs are designed for fast heat transfer applications, and packages without DAP are designed for applications that require slower response rates. The fast thermal response rate allows the temperature sensor to respond quickly to any temperature change, providing accurate readings.
Design Guidelines - Bottom Installation
The sensor location should be as close as possible to the heat source to be monitored. Perforations or cuts in the PCB between the thermal IC and the temperature sensor should be avoided as this may slow or prevent thermal response. If possible, install the temperature monitor on the bottom of the PCB directly below the heat source.
TI recommends using vias to transfer heat quickly from one side of the PCB to the other because vias have better copper thermal conductivity than FR-4. You can use as many parallel vias or filled conductive vias as possible to transfer heat from the heat source to the temperature monitor for fast thermal balance between the two ICs. A QFN or DFN package with DAP helps to further reduce the thermal resistance path between the via and the sensor die.
Design Guidelines - Formation Considerations
If placing the temperature sensor on the other side of the heat source is impractical or uneconomical, place it on the same side as close to the heat source as possible.
The most efficient way to establish a thermal balance between the heat source and the temperature monitor is to use the formation. A solid floor that extends from the heat source to the temperature sensor should be used.
Temperature monitoring is critical in PCB designs with thermoelectric regions or high-power ICs. It is necessary to evaluate whether the selection of the local temperature sensor complies with the system requirements and protection scheme of the relevant design.
The sensor position and high thermal conductivity path should be considered to establish a rapid thermal balance between the sensor and the heating element.
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