A5974AD datasheet(28/49 Pages) STMICROELECTRONICS

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Application information

A5974AD

28/49

Doc ID 018762 Rev 1

where TRISE and TFALL represent the switching times of the power element that cause the

switching losses when driving an inductive load (see Figure 14). TSW is the equivalent

switching time.

Figure 14.

Switching losses

●

Quiescent current losses.

Equation 25

where IQ is the quiescent current.

Example:

–VIN = 12 V

–VOUT = 3.3 V

–IOUT = 2A

RDS(on) has a typical value of 0.25 @ 25 °C and increases up to a maximum value of 0.5. @

150 °C. We can consider a value of 0.4

Ω.

TSW is approximately 70 ns.

IQ has a typical value of 5 mA @ VIN = 12 V.

The overall losses are:

Equation 26

The junction temperature of the device is:

Equation 27

⋅

TOT

DSON

OUT

()

⋅

OUT

⋅

⋅⋅

⋅

0.4 2

0.3

12 2 70 10

–

500 10

12510

–

⋅⋅

⋅

⋅⋅

1.38W

≅

thJA

TOT

⋅

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