AN2386 Datasheet, PDF (1/30 Pages) STMicroelectronics – How to achieve the threshold voltage thermal coefficient

AN2386
Application note
How to achieve the threshold voltage thermal coefficient
of the MOSFET acting on design parameters
Introduction
Today, the MOSFET devices are used mainly as switches in electronic circuits. In such
operational conditions, the MOSFET device works in switch on and switch off modes.
However, in some applications, as in audio amplifiers or air conditioning, the MOSFET
works in a linear zone. The MOSFET works in a linear zone when either it is subject to a
high voltage, or a high current passes through the device. As it is well known in literature,
during the linear zone operation mode the MOSFET could fail if a thermal run-away occurs.
The failure conditions depend on either of the internal structure of MOSFET or of the
package used. The threshold voltage thermal coefficient (TVTC) is one of the big elements
that could bring the MOSFET to fail. TVTC is achieved deriving the MOSFET threshold
voltage against the temperature. TVTC is a negative coefficient because of when the
temperature increases the threshold voltage decreases. When TVTC increases in absolute
value, the MOSFET becomes thermally instable and a failure could occur. Therefore, in
order to understand if a MOSFET device can be used in an application working in linear
zone in safety conditions, a device with a low TVTC value must be considered and, thus, it is
important to achieve a theoretical expression for it.
June 2006
Rev 1
1/30
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