Cyclone III FPGA Temperature Measurement.....

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In our board schematics, we don't have a on-board temperature sensing device.

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Ok.

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We have only one component ADM1185, which is a supply monitor and sequencer.

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I looked at the data sheet. If it had an unused ADC channel, I was going to suggest using a voltage output temperature sensor, however, the ADM1185 uses comparators for voltage monitoring.

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then we dont have any option to measure even on-board temperature also.

So we are planning to go for some external to measure it.

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If you have some FPGA pins available for GPIO (that you can access with a soldering iron :) ), then an I2C sensor or SPI sensor could be added to the design easily. There are adhesive SMT footprints that you can stick to the PCB, and then solder an ADM1032 I2C sensor, or AD7814 SPI temperature sensor. If you use the ADM1032 sensor, then it has local and remote sensing, so you could bond a diode-connected-transistor to the FPGA (or its heatsink).

Cheers,

Dave