AN1172

How to calculate the junction temperature during clamping periods

21/23

Figure 23. shows the maximum

factors. Calculations are similar whatever the package is (TO92, DIL20, SOT223), because

in such a range of times, the Zth is only due to the die area.

Note that

level (taken equal to its worst value: 60 mA). So, when the load RMS current increases, the

decreases because of the load series inductance decrease (here the turn-off current is

Figure 23.

Supplementary temperature rise at clamping depending on load nature

(for ACS402-5SB4 or ACS108-5SX)

It can be concluded that, if the junction temperature was 110° C before turn-off, the

maximum transient temperature can reach 160° C. As these events last less than one ms

(refer to Figure 22.), such junction temperatures can be permitted.

C.3

Repetitive clampings

To evaluate heating due to repetitive clampings, Equation C6 can be used, assuming that

the clampings occur at a constant period T and that the conduction losses can be neglected

in front of the previous ones.

Equation C6

In practice T (above 1s) is very much higher than the clamping duration. Equation C6 can

then be simplified to the following one.

Equation C7

60

45

cos

=0.1

ϕ

cos

=0.7

ϕ

cos

=0.9

ϕ

cos

=0.98

ϕ

30

0

0.1

0.2

0.3

0.4

0.5

15

IRMS (A)

⎥

⎦

⎤

⎢

⎣

⎡

-

+

-

-

+

⎟

⎠

⎞

⎜

⎝

⎛

-

-

+

-

⋅

=

∆

)

t

t

(

Zth

)

T

(

Zth

)

t

t

T

(

Zth

T

t

t

1

Rth

T

t

t

I

V

2

1

T

0

ZC

0

ZC

0

ZC

0

ZC

H

cl

rep

Rth

T

t

t

I

V

2

1

T

0

ZC

H

cl

rep

-

⋅

=

∆