L6223 datasheet(12/33 Pages) STMICROELECTRONICS

12 / 33 page

SHIFT REGISTER bITS

Full/Simpl.

Operation

Mode

Close Loop

Frequency

(kHz)

Open Loop

t(ON) [%]

Close Loop

Current

Level [%]

100

85%

40%

70%

55%

85%

DISABLED

40%

DISABLED

70%

DISABLED

55%

DISABLED

85%

40%

70%

55%

85%

100

40%

100

70%

100

55%

100

85%

40%

70%

55%

85%

DISABLED

40%

DISABLED

70%

DISABLED

55%

DISABLED

85%

L6223 Operating Configuration vs. 6bits Shift Register Programming (Continued)

APPLICATION INFORMATION

Single Device Application

Figure 10 shows a typical Single Device Applica-

tion. With the shown external RC network, the

higher chopping frequency is 20 kHz.

In the figure 11, 12 and 13 are shown the wave-

forms required to drive the motor in Half/Full Step

in FULL MODE OPERATING (FMO) and SIMPLI-

FIED MODE OPERATING (SMO). The sense re-

sistor defines the total motor current. This means

that when two phases are ON, the sense current

is two times the phase current. In this case the

sense resistor value is RS =(Vref/2Ip), where Vref

is the reference voltage and IP the phase current.

We have supposed that the phase current is of

the same intensity in the two phases. When only

one phase in ON, the current flowing in the sens-

ing resistor is the phase current: this occurs in

half step driving mode. The Figures 14 and 15

show the envelope of the sensing voltage in full

and half step respectively.

When current imbalance is not considered, this

envelope represents the current level 2Ip control-

led by the chopping when L6223 is working at

100% of current; in full step this level is constant

while in half step two different levels are present

(Figure 15). Actually, in full step two phases are

always ON, and the chopping current level can be

changed only by the controller. In half step when

two phases are ON and L6223 is working at

nominal current level (2Ip), but when only one

phase is ON, L6223 selects automatically the re-

duced current. This level depends upon the pro-

gramming bits. In Figure 15 the higher level rep-

resents the chopping at nominal value (two

phases ON), the lower level the chopping at the

reduced current (one phase ON). The negative

peak shown in the figures represents the fast cur-

rent recirculation at the phase change.

Fig. 15 shows also what happens when the re-

duced current level selected is at 70% of the

nominal value. The motor torque is proportional to

the vectorial sum of the phase currents: it can be

seen that the unipolar stepper motor control actu-

ated by L6223 in half step is at constant torque

but not at constat current.

L6223

12/33

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