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Remote Temp Click is a temperature sensing Click board™, which features the EMC1833 from Microchip, a specifically designed IC, capable of measuring remote temperature. This option makes Remote Temp Click well-suited for monitoring the temperature of a CPU, GPU or FPGA, where the BJT model junction can be a substrate PNP or NPN. Remote Temp Click can be configured to measure a CPU substrate transistor, a discrete 2N3904 thermal diode, or CPU/GPU processor diode. The diodes can be connected as indicated in the figure below. The EMC1833 can also report an ALERT signal if programmed temperature thresholds are exceeded.
Remote Temp Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.
The EMC1833 features a high accuracy of ±1°C within the range between -40°C and +125°C, which is a critical thermal bandwidth of most IC with the substrate PNP or NPN transistor as a temperature sensor. However, the Click board™ can be operated within the range between -40°C to +125°C when used to measure the Internal/External temperature. Features such as dual temperature measurement, high accuracy, and programmable ALARM events, allow this Click board™ to be used in many applications, including dual-zone thermal monitoring in FPGA, embedded, and PC systems, i.e. when it is required to monitor both the ambient temperature within the enclosure, as well as the IC die temperature, for test and measurement applications, and similar.
The main component of the Remote Temp Click is the EMC1833, a ±1°C, SMBus/I2C compatible local/remote temperature sensor with an overtemperature alarm, produced by Microchip. This sensor is capable of measuring its own temperature, as well as the temperature of the remote BJT junction, which can be either a discrete PNP or NPN transistor, or a substrate of some integrated component (typically CPU, FPGA, ASIC or GPU).
There are some specific requirements for a discrete component when using it as a remote temperature sensor: for example, it has to be a small signal BJT. For more information, please refer to datasheet of the EMC1833, which also states some forward voltage ranges for the highest and the lowest expected temperatures and other parameters which should be considered when selecting the transistor. The discrete component can be connected to the screw terminal at the edge of the Click board™.
The EMC1833 features a 11-bit ADC which results in having the 0.125°C resolution. The temperature measurement results are stored in the internal and external temperature registers. Both external and internal temperature measurements are stored in 11-bit format with the eight Most Significant bits (MSb) stored in a high-byte register and the three Least Significant bits (LSb) stored in the three MSB positions of the low-byte register. All other bits of the low-byte register are set to zero. The EMC1833 IC automatically sends biasing current through the BJT junctions, while the IC samples the forward voltage for the given current and calculates the temperature. The ADC integrates the result over a period of 21ms, reducing the noise that way. Therefore, the temperature acquisition is not particularly fast. In return, the temperature measurement results are more accurate and reliable.
The accuracy of the remote measurement depends on the ideality factor of the remote BJT junction. Not all external diodes, processor or discrete, will have this exact value. This variation of the ideality factor introduces errors in the temperature measurement which must be corrected for. Therefore, the EMC1833 features Programmable External Diode Ideality Factor, which can be easily set by changing the value in the appropriate register.
The EMC1833 IC also features the ALERT reporting capability. If a programmed threshold is exceeded, the ALERT pin will be asserted to a LOW logic level. When the ALERT pin is asserted, it will remain latched until its STATUS register is read after the overtemperature condition no longer exists. Another way to clear the ALERT interrupt is to respond to the alert response address. This is a global I2C/SMBus protocol, where the host MCU broadcasts a Receive Byte transmission after the interrupt is received. One (or more) peripheral devices which generated this interrupt will respond, sending their I2C peripheral address, following the bus arbitration rules. This protocol is explained in more details within the EMC1833 datasheet. The ALERT pin is routed to the INT pin of the mikroBUS™ and it is pulled up by a resistor.
The peripheral address decode is performed by pulling known currents from the VDD pin through the external resistor, causing the pin voltage to drop based on the respective current/resistor relationship. This pin voltage is compared against a threshold that determines the value of the pull-up resistor.
This Click board™ is designed to be operated only with 3.3V logic level. A proper logic voltage level conversion should be performed before the Click board™ is used with MCUs with logic levels of 5V. It is ready to be used as soon as it is inserted into a mikroBUS™ socket of the development system.
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