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Programmable Single Chip, Dual Thermal Monitoring Device for use with Forward Biased Annular Diodes Disclosure Number: IPCOM000200048D
Publication Date: 2010-Sep-24
Document File: 5 page(s) / 109K

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Programmable thermal monitoring device that utilizes annular diodes present in PowerPC silicon to accurately monitor operational temperatures.

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Programmable Single Chip, Dual Thermal Monitoring Device for use with Forward Biased Annular Diodes

Construction of the internal annular diode (as in IBM's PowerPC 970 class processors) precludes the use of off-the-shelf monitoring solutions. Typical off-the-shelf solutions (like Maxim's MAX6656 and Analog Devices' ADT7467) forces two currents, calculates the corrective ideality factor and then uses this corrected ideality factor to calculate the temperature. The situation with the diodes in PowerPC 970 family, is that its ideality factor isn't constant with temperature as assumed by the temperature sensing part. Off-the-shelf solutions are also geared to work with 'diodes' created from a substrate PNP, with the collector connected to ground, using the base and emitter as the cathode and anode. The PowerPC970 family uses a true diode within the substrate.

The only approach to solve this problem is to devise a solution that creates a constant current source, apply it to the diode and monitor the change in voltage with respect to temperature. Using two pre-calibrated temperature verse voltage points (done for each chip at WFT/MFT and stored internally in a fused array), a slope can be determined and used to calculate temperature for any given voltage drop across the diode. Temperature change is a linear function with respect to voltage change.

A discrete solution can devised but has these drawbacks:

Multiple discrete devices need to be interconnected to perform thermal monitoring function (duplicated or multiplexed for each thermal diode):

Separate constant current source required (operation amplifier circuit) Separate gain amplifier (possibly) required
Separate Analog to Digital (high precision 13 bit) converter required
Optional programmable device (which includes digital logic and possibly software control) needed to perform:
slope calculation for temperature conversion,
warning and critical temperature monitoring
user input/output interface
serial communication interface for parameter entry (calibration points) and status monitoring
and/or optional parallel interface for visual display (i.e. Liquid Crystal Display)

Using multiple devices requires larger board (PCB) area, higher bill of materials parts count, potentially higher failure rate and possibly higher implementation costs.

By using a programmable analog/digital device (Cypress Microsystems' PSoC CY8C27433 ), a single chip solution can be devised (see Figure 1) that supports monitoring of two thermal diodes, provides a serial interface for configuration and status as well as a parallel interface for a 2x16 character LCD. The Cypress Microsystems PSoC device provides all the necessary analog and digital building blocks as well as a generic 8-bit microprocessor. The analog blocks are properly configured to provide the necessary functions like a constant current source, gain amplifier and multiplexor (see Figure 2). The digital blocks are properly configured to provide the Analog...