DocID14109 Rev 3

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AN2650

Power dissipation

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7

Power dissipation

The calculation of the power dissipation depends upon the selected slew rate and decay

mode of the device. In Figure 12 the set up was selected with a fast decay.

Figure 12. Current flow and voltage drop during fast decay

For a rough calculation of the power dissipation, three different phases are selected:

1.

Static ON

2.

Static free wheeling (FW), fast decay

3.

Dynamic on and off with slew rate.

7.1

Static ON

Only the RDS,on of the high and low side switches are used for generating power

dissipation.

t

Vs

V

OUT-A

V

OUT-B

t

PWM

Vs

gnd

ON

ON

OFF

OFF

I

L

Vs

gnd

ON

I

L

OFF

ON

OFF

ON

FW fast decay

OUT-B

OUT-B

A

-

T

U

O

A

-

T

U

O

t

D

t

Pulse

t

r/f