ANALOG DEVICES EE-346 Service Manual

Engineer-to-Engineer Note EE-346

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The o n-chip thermal diode discussed throughout this EE-Note app lies to ADSP-214xx SHARC

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Using the On-Chip Thermal Diode on Ana l og Dev ic es P r ocessors

Contributed by Mitesh Moonat Rev 2 – August 2, 2010

Introduction

As a processor’s speed increases, heat dissipat ion also increases. This results in an increased operat ing
temperature. For processors that operate at higher speeds, thermal management is important to ensure
reliable operation and longer life. ADSP-214xx SHARC® processors incorporate an on-chip thermal
diode that can be used to monitor the die temperat ure and take appropriate actions if it goes beyond a
thr es hold va lue .

processors only (for ADSP-2147x processors, the thermal diode is only available in the 100­LQFP_EP package. See the device data sheet for more details
processors from the exi s ting portfolio today incorporate an on-chi p therma l diode.

This EE-Note describes how the on-chip thermal diode can be interfaced with a digital temperature
sensor. Example code is also pr ovided in the asso ciated .ZIP fi le for the thermal diode and the ADM1032
inte rfa c e on the various ADSP-214xx evaluation boards.

[3]

). No other A

Thermal Diode on SHARC Processors

The t hermal diode on ADSP-214xx processors is a grounded collector, PNP bipolar junction transistor
(BJT). The THD_P pin is connected to the emitter and the THD_M pin is connected to the base of the
transistor. These pins should be connect ed to the D+ and D- pins of the sensor being used. For details on
the thermal diode, refer to t he ADSP-2146x SHARC Processor Hardware Reference

[1]

.

Digital Temperature Sensor

Analog temperature sensing techniques such as using thermistors, resistance temperature detectors
(RTDs), and t her mocouples require external signal conditioning and an analog-to digital converter (ADC).
In contrast, a number of silicon-based temperature-sensing ICs output precise digital representations of the
temperatures they are measuring. These are ca lled digital temperature sensors. Most of them connect to a
remote diode present on the chip whose temperature is to be measured, and use is based on following
principle:

“Change in the VBE (base-to-emitter voltage) when the diode is operated at two different currents is
directly related to the absolute temperature”.

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