L6223 datasheet(18/33 Pages) STMICROELECTRONICS

18 / 33 page

Use of the Programming Mode

A typical application of the L6223 requires driving

the motor according to Fig. 23a and Fig. 23b.

Starting from t0 =t5 and continuing until t1 the mo-

tor is kept in stand-by; at time t1 begins an accel-

eration period that is completed at time t3. The

motor then is driven at a contant speed until t4,

when the speed is decelerated and is stopped at

t5 =t0 for a new standby period.

During these events the L6223 can be pro-

grammed several times for different working

modes. The most important parameter is the cur-

rent through the windings of the stepper: at the

time t0;t1;t2;t3 and t4 the current can be modi-

fied, for example, as it is shown in Fig. 23b. This

behaviour allows the best motion control and, at

the same time, optimizes efficency of the power

output block of the I. C.

But this is not the best in terms of performances

by programming: in fact, between t1 and t5 the de-

vice can be programmed to work in Closed Loop

and to chop at half of the RC oscillator frequency

during the time t3 to t4. In the stand-by condition

the I. C. can be programmed to work in Open

Loop mode where the current can be fixed by the

reduction of the minimum TON time (75% or 50%)

defined by the discharge time of the RC oscillator.

Of course in this way the current can be modified

by Supply Voltage changes; the same is not pos-

sible in Closed Loop operation where the device,

in order to keep the windings current constant,

modifies the TON time: wide at low VS and narrow

at high VS. This is the reason why when the motor

is driven at a constant speed (t3 to t4) with small

current and high Supply Voltage, it could become

necessary to program the lower chopping fre-

Figure 23: a,b) Speed profile and motor current

control change for the best efficency of the I.C.

c,d) Current control change by using DA/CLEV

input only, during the stand-by period.

quency to allow a suitable TON width otherwise

the current of the windings would go out of con-

trol.

The motion profile, shown in Fig. 23a can be ob-

tained when preferred, with only two program

changes actuated while the motor is in stand-by.

The current becomes as shown in Fig. 23c. The

device can be programmed at t0 =t5 for Imotor =

55% (stand-by) and at t1 for Imotor = 70%: for both

the actuations, the DA/CLEV is kept high to allow

the program change, while, by keeping it to zero

during t1 -t3 and t4 -t5, the current is automat-

ically select as 100% (Fig. 23d). During t3 -t4 the

current is reduced according to the percentage

programmed at the time t1.

Power dissipation (Simplified method of calcula-

tion).

Here below the Full Step Operating Mode is con-

sidered; in addition, the following working condi-

tions have been taken up:

1) Constant speed rotation of the driven unipolar

stepper Motor.

Figure 22: Pover output configuration.

L6223

18/33

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