TDA1154 datasheet(4/6 Pages) STMICROELECTRONICS

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Figure 4. Application circuit

If Eg and Rm are motor back electromotive force and

motor internal resistance respectively, then:

Eg + R m Im

= Rt [I (5)+

V(ref)

]

+ V(ref) (b)

From figure 2 it is seen that:

(8) = Im +

V(ref)

(c)

Subsituting equations (a) and (c) into (b) yields:

= Im [

− Rm ] +

+ V(ref) [

( 1 +

)+ 1 ] + Rt IO (5)(d)

The motor speed will be independent of the resist-

ing torque if Eg is also independentof Im. Therefore,

in order to determine the value of Rt term(1) in (d)

must be zero:

= KR m (K = 20)

If Rt

> KRm, an instability may occur as a result of

overcompensation.

The value of RS is determinated by term (2) in (d)

so as to obtain he back electromotive force (Eg)

corresponding to required motor speed:

RS = Rt

V(ref) (1 + 1 / K)

Eg − V(ref) − Rt IO (5)

≅

≅ Rt

V(ref)

− V(ref) − Rt IO (5

)

Where V(ref) = 1.2V and IO (5) = 1.7 mA

(1)

(2)

TDA1154

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