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Junction Temperature Validation using an A/D and a Voltage Proportional to Temperature Circuit

IP.com Disclosure Number: IPCOM000007644D
Original Publication Date: 2002-Apr-10
Included in the Prior Art Database: 2002-Apr-10
Document File: 4 page(s) / 33K

Publishing Venue

Motorola

Related People

Andrew Lillie: AUTHOR [+2]

Abstract

Junction temperatures and self-heating of semiconductor devices can be measured using an A/D and voltage proportional to temperature circuit. These circuits are calibrated so that an increase in temperature of one degree Kelvin is proportional to one least significant bit of the A/D. While the part is idle and consuming very little current the A/D and temperature circuits are calibrated to a specific ambient temperature and the conversion result recorded. Then, while maximum current is being consumed by the operating part, a second conversion is performed until the conversion result is stable. The difference between idle and operating mode results represents the self heating of the part when consuming current and is the temperature to which the device junctions are elevated above ambient when operating.

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Junction Temperature Validation using an A/D and a Voltage Proportional to Temperature Circuit

 

Andrew Lillie and Randy Dees

 

Abstract

Junction temperatures and self-heating of semiconductor devices can be measured using an A/D and voltage proportional to temperature circuit. These circuits are calibrated so that an increase in temperature of one degree Kelvin is proportional to one least significant bit of the A/D.  While the part is idle and consuming very little current the A/D and temperature circuits are calibrated to a specific ambient temperature and the conversion result recorded.  Then, while maximum current is being consumed by the operating part, a second conversion is performed until the conversion result is stable.  The difference between idle and operating mode results represents the self heating of the part when consuming current and is the temperature to which the device junctions are elevated above ambient when operating.

Semiconductor devices are required to operate at specified junction temperatures. Circuit operation at these temperatures must be tested in production at an ambient temperature (TA) chosen to ensure a junction temperature (TJ) that meets the specified requirements. The ambient temperature applied is critical because of the effect of temperature on product yield at production test.

Currently assumptions are made for the thermal resistance between the junction and ambient temperatures (qJA) and power dissipated (PD) to determine a TA sufficient to guarantee a required TJ, equation (1).

TJ = TA + (qJA  x PD)

(1)

There are several issues with this method:

·        qJA in the test environment at a given temperature is unknown and will be different to the apparatus used to estimate qJA. Load-boards, tester heads, the number of tester channels used all affect qJA.

·        qJA is dependent on the die size and package used so that the same qJA can not be used for a family of products.

These issues result in assumptions and are a cause of error when determining an appropriate ambient temperature under which to conduct production test at a given junction temperature.

Using an analog to digital converter (A/D) and a voltage proportional to temperature circuit the junction temperature of the part can be determined independently of the test fixture and environment. The voltage proportional to temperature is linearly proportional to tem...