F1206A0R20FSTR datasheet(19/23 Pages) AVX

19 / 23 page

Fig. 2c. Choice of 0.75A fuse, example #2.

Pre-arcing I2t

Maximum I2t design rule

I2t for sample switch-on pulse

Accu-Guard®

SMD Thin-Film Fuse

l max.

Fig. 1a. Sine wave pulse parameters for Joule

integral calculation, example #1.

Thus, for the current pulse in Figure 1b, the Joule integral is

[(4.8A)2 x 7.7 x 10-6 sec]/2 = 8.9 x 10-5 A2 sec.

The pulse duration is 7.7μsec. We must find a fuse that can

absorb at least 8.9 x 10-5 X 2 = 1.8 x 10-4 A2sec Joule inte-

gral within 7.7 μsec without actuation. According to the I2t

graph on page 6, pre-arcing Joule integral is 2.3x10-4 A2sec

for the 0.5A fuse, which is slightly more than needed. The

next lower rating (0.375A), has only 6x10-5 A2sec, which is

not enough. Therefore, 0.5A fuse should be chosen for this

application, see Figure 1c.

FUSE PRE-ARCING JOULE INTEGRALS

vs. PRE-ARCING TIME

2. Triangular current pulse

The Joule integral for triangular pulse is

[(Imax.)2 x t]/3,

see Fig. 2a.

Fig. 2a. Triangular pulse parameters for Joule

integral calculation, example #2.

l max.

Thus, for the current pulse in Figure 2b, the Joule integral is

[(1.5A)2 x 3 x 10-3 sec]/3 = 2.25 x 10-3 A2sec.

Fig. 1b. Sine wave pulse, example #1.

Fig. 2b. Triangular pulse, example #2.

The pulse duration is 3 msec. In the I2t graph on page 6, pre-

arcing Joule integral for 3 msec pulse is 4 x 10-3A2sec for the

0.5A fuse (not enough) and 2 x 10-2 for the 0.75A fuse (more

than enough). Therefore, 0.75A fuse should be chosen for

this application, see Figure 2c.

FUSE PRE-ARCING JOULE INTEGRALS

vs. PRE-ARCING TIME

0.75A

PRE-ARCING TIME l2t, A2 sec

PRE-ARCING TIME, sec

100

10-1

10-2

10-3

10-4

10-5

10-7

10-6

10-5

10-4

10-3

10-2

10-1

110

μsec/div

1A/div

2 msec/div

0.5A/div

0.5A

PRE-ARCING TIME l2t, A2 sec

PRE-ARCING TIME, sec

100

10-1

10-2

10-3

10-4

10-5

10-7

10-6

10-5

10-4

10-3

10-2

10-1

110

Fig. 1c. Choice of 0.5A fuse, example #1.

Pre-arcing I2t

Maximum I2t design rule

I2t for sample current pulse

DESIGNING FOR CURRENT

PULSE SITUATIONS

1. Sine wave current pulse

The Joule integral for sine wave pulse is

[(I

max.)

2 x t]/2,

see Fig. 1a.

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