AN2689 datasheet(31/42 Pages) STMICROELECTRONICS

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AN2689

Supply rail protection

Doc ID 14310 Rev 3

31/42

So, C = 20.35 mF.

Hence:

Then, thanks to the test curves from the load dump generator, the result is tp = 33.6 ms and

Rd = 0.22 .

From the equations in Section 4.5 on page 29, Vcl = 33.8 V and Ipp = 26.6 A, which means

the residual over voltage will be consistent with the admissible maximum voltage of the

module to protect.

4.5.2

Power dissipation determination

The peak power dissipation in the Transil will be:

Figure 42, shows that for 33.6 ms exponential surge duration the maximum admissible

power the RBO40-40 can withstand is approximately 900 W.

Figure 42.

Peak pulse versus exponential surge duration

Figure 43. shows the derating factor for the ambient temperature effect.

Figure 43.

Relative variation of peak power versus junction temperature

()

RBO

120

nom

⎟⎟⎠

⎞

⎜⎜⎝

⎛

Ppp

Ipp

Vcl

Ppp

549.25 W

⇒

100

0.1

0.2

0.5

1.0

2.0

5.0

10.0

Transil T1

Transil T2

tp(ms)

Ppp(kW)

100

125

150

175

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Tj initial (°C)

Ppp[Tj]/Ppp[Tj initial=85°C]

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