11.3.2. External Temperature Sensing Diode
The Stratix® V external TSD requires two pins for voltage reference. The following figure shows how to connect the external TSD with an external temperature sensor device, allowing external sensing of the Stratix® V die temperature. For example, you can connect external temperature sensing devices, such as MAX1619, MAX1617A, MAX6627, and ADT7411 to the two external TSD pins for Stratix® V device die temperature reading. The TSD diode is a substrate or common collector PNP diode type.
The TSD is a very sensitive circuit that can be influenced by noise coupled from other traces on the board or within the device package itself, depending on your device usage. The interfacing signal from the Stratix® V device to the external temperature sensor is based on millivolts (mV) of difference, as seen at the external TSD pins. Switching the I/O near the TSD pins can affect the temperature reading. Altera recommends taking temperature readings during periods of inactivity in the device or use the internal TSD with built-in ADC circuitry.
The following are board connection guidelines for the TSD external pin connections:
- The maximum trace lengths for the TEMPDIODEP /TEMPDIODEN traces must be less than eight inches.
- Route both traces in parallel and place them close to each other with grounded guard tracks on each side.
- Altera recommends 10-mils width and space for both traces.
- Route traces through a minimum number of vias and crossunders to minimize the thermocouple effects.
- Ensure that the number of vias are the same on both traces.
- Ensure both traces are approximately the same length.
- Avoid coupling with toggling signals (for example, clocks and I/O) by having the GND plane between the diode traces and the high frequency signals.
- For high-frequency noise filtering, place an external capacitor (close to the external chip) between the TEMPDIODEP /TEMPDIODEN trace. For Maxim devices, use an external capacitor between 2200 pF to 3300 pF.
- Place a 0.1 uF bypass capacitor close to the external device.
- You can use the internal TSD with built-in ADC circuitry and external TSD at the same time.
- If you only use internal ADC circuitry, the external TSD pins (TEMPDIODEP /TEMPDIODEN ) can be connected to GND because the external TSD pins are not used.
For details about device specification and connection guidelines, refer to the external temperature sensor device datasheet from the device manufacturer.
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