8

where the case of a Power MOSFET is defined at the point of contact between the drain lead(s)

and the mounting pad surface. R

turer independent of the application and mounting method and is therefore the best means of

comparing various suppliers component specifications for thermal performance. On the other hand,

it is difficult to quantify R

sheet thermal data, the user should always be aware of the test conditions and justify the compat-

ibility in the application.

Appendix B

Thermal Measurement

Prior to any thermal measurement, a K factor must be determined. It is a linear factor related to

the change of intrinsic diode voltage with respect to the change of junction temperature. From the

most Power MOSFET devices.

Figure 6. K factors, slopes of a V

After the K factor calibration, the drain-source diode voltage of the device is measured prior to any

heating. A pulse is then applied to the device and the drain-source diode voltage is measured

30us following the end of the power pulse. From the change of the drain-source diode voltage, the

K factor, input power, and the reference temperature, the time dependent single pulsed junction-to-

reference thermal resistance can be calculated. From the single pulse curve on figure 7, duty

cycle curves can be determined. Note: a curve set in which R

was characterized using the ambient as the thermal reference. The board layout specified in the

data sheet notes will help determine the applicability of the curve set.

NDS9956 V

vs Temperature

25

50

75

100

125

150

0.2

0.3

0.4

0.5

0.6

0.7

Temperature (°C)

5mA

2mA

1mA

10mA

I

= 20mA

SD

1mA = 2.39 mV/°C

2mA = 2.33

5mA = 2.25

10mA = 2.19

20mA = 2.13

V

= 0V

GS

SD