L6223 datasheet(20/33 Pages) STMICROELECTRONICS

20 / 33 page

RDSON L=

α 1.2 = 2Ω

RDSON H=

α 0.7 = 1.15Ω

RS = 0.36

Ω

Rtot = 12.5

Ω

VON = 26.24V

(During the chopping)

VOFF = 9.7

(During the chopping)

DC = 15.6%

Tp = 8 msec

T1 = 250

µs

(During the phase change)

PdL = 1.1W

PdH = 0.4W

Pdch = 0.20W

Pdo = 0.24W

At last:

Ptot = 1.94W

The needed thermal resistance between junction

and ambient must be equal to:

Rthj−amb =

Tjmasc

− Tambmasc

Ptot

≅ 39°C/W

The worst case here considered requires an

heatsink of 25

°C/W. The calculation of the power

dissipation by considering the current imbalance

and by simulating a typical motion needed to

carry the head of a printer for example, becomes

full of difficulties. The use of the Personal Com-

puter is helpful in such a case: few examples are

shown from Fig. 28ab until Fig. 31 ab.

Each figure shows the Application Datas and one

diagram where the Total Dissipated Power versus

the peak of the motor current is plotted.

A max Ambient temperature of 70

°C and a max

junction temperature of 150

°C have been consid-

ered for a few applications using one single de-

vice and a dual device configuration to drive one

Figure 24: Motor current Ip during tON (phase MA; Q5 and RS sre common whit the phase MB).

Figure 25: Slow decay of the motor current Ip/2 during toff (phase MA).

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