AN604 datasheet(9/12 Pages) STMICROELECTRONICS

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AN604

An application example

Doc ID 3607 Rev 3

9/12

3.1

Average and rms current calculation

The first step is the calculation of the average and rms currents.

The forward average current is the output current: IF(AV) = Iload = 4.7 A.

As illustrated in Figure 6, the forward current has a trapezoidal shape. The formula to

calculate the rms current of trapezoidal waveform is given in Figure 4. IF(RMS) is then:

Equation 15

3.2

VT0 (Tj) and RD (Tj) calculation

The second step is the calculation of VT0 (Tj) and RD (Tj) in the application condition range.

Figure 7.

STPS30M100S forward voltage drop versus forward current

Tjref1 = 25 °C and Tjref2 = 125 °C. To calculate maximum conduction losses, read maximum

values of VF at IMin and IMax in Figure 7. This figure is available in the STPS30M100S

datasheet. These values are summarized in Table 1.

() ( )

6.4 A

0.6

11.8

F(RMS)

⋅

Table 1.

VF(Max) values at IMin and IMax

IF (A)

VF(Max)(IF, 25 °C) (V)

VF(Max)(IF, 125 °C) (V)

IMin = 4

0.52

0.43

IMax = 11.8

0.63

0.55

I Min = 4A

I Max = 11.8A

0.43V

0.55V

0.63V

0.52V

(Typical values)

T = 125 °C

(Maximum values)

T = 125 °C

(Maximum values)

T = 25 °C

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