AN4242 datasheet(7/26 Pages) STMICROELECTRONICS

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AN4242

Features of the SiC diodes

1.3.2

“C” thermal coefficient

The “C” thermal coefficient represents the leakage current dependence on the junction

temperature. The leakage current increases by an exponential law with the junction

temperature. Knowing a reference point IR(VR,TjRef) and the value of the thermal coefficient

“C”, one can easily calculate the leakage current at a given temperature Tj using the

following formula:

Equation 7

where VR is the reverse voltage applied across the diode.

Each diode has its own coefficient that can be calculated using two points as follows:

Equation 8

If the SiC Schottky diodes have low leakage currents and they have also a smaller

temperature dependence compared to the Si counterparts. As illustrated in Table 2, typically

the “C” thermal coefficient should be around 2 times lower than the Si diodes.

The feature of low dependence with the Tj is interesting to push back the limit of thermal

runaway due to the power reverse losses. Regarding the stability criterion formula linked to

PPREV given by Equation 9, the interest for the use at high Tj of small packages with high

thermal resistance becomes certain.

Equation 9

Table 2. “C” thermal coefficient comparison between Si and SiC diode

Product

IR1 @ VR = 400 V, Tj1IR2 @ VR = 400 V, Tj2

C coefficient

STTH8R06

8 µA @ 125 °C

50 µA @ 150 °C

0.070

STPSC8H065D

4 µA @ 150 °C

8.5 µA @ 175 °C

0.030

I (V ,T ) = I (V ,T

) · e

jRef

c(T - T

)

jRef

c =

T- T

jRef2

jRef1

· ln

I(V,T

)

jRef2

I(V,T

)

jRef1

(T )

dTj

Rth(j-a)

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