Position Feedback.

As shown in Figs. 3 and 6, a positive error voltage

VERR = VCOM - VFBK drives the motor with a

positive M+ voltage with respect to M-. A correct

negative electro-mechanical feedback is estab-

lished when the motor, supplied with a positive

M+ voltage with respect to M-, drives the feed-

back potentiometerwiper to Vcc.

Rest Zone.

When the differential input voltage VERR crosses

the zero Volts threshold, as detected by the preci-

sion comparator COMP1, the motor is braked by

driving it with a zero Volts voltage.

As long as VERR is kept inside the Rest Zone,

ranging from -VSTR to +VSTR (see Figs. 1 and

2), no electrical stimulus is applied to the motor

terminals. When in the Rest Zone M+ and M- are

both driven to Vcc.

Running Zone.

When the input error voltage VERR goes out of

the Rest Zone (see Figs. 1 and

2) the motor

starts and the wiper voltage VFB of the feedback

potentiometer moves in the direction of the input

voltage VCOM, bringing the VERR voltage back

to zero.

When VERR becomes lower than (Vcc-VSTP)/10,

a proportional control activates. The motor volt-

age at M+ and M- lowers with a rate factor of 10

times VERR. This motor voltage is generated, ac-

cording to the motor direction, by connecting to

Vcc one motor terminal and by switching the op-

posite one with a PWM control.

When

approaching

the

target

position,

at

VERR=0, the motor jumps into the Rest Zone

from a residual VSTP supply voltage. This control

is suitable for motors that still run with the min.

VSTP=2.5V residual supply voltage in all condi-

tions, ensuring that the rest position is finally

reached. But at the same time the

max.

VSTP=3.5V should not make any motor run too

fast and stop far away from the set point for me-

chanical inertia, or even get out of the rest zone

possibly starting oscillations.

Time Out Counter.

The Time Out is performed by a 14 Bit Counter

that counts 16384 Tosc periods. When the input

error voltage VERR goes out of the Rest Zone the

motor and the counter start. The motor stops at

the VERR zero crossing or when the Counter

times out, whichever comes first.

Direction Control.

The motor can be driven in both direction and

stopped by the timer as shown in Fig. 7.

The bias voltage at VFB input sets the threshold

voltage for the direction control input pin (DIR).

VFB and VCOM inputs may be swapped causing

the motor to reverse directions.

M

-

-

+

+

M+

M-

VFB

VCOM

U709

Vcc

GND

Vcc

Figure 3. L9909 Simplified Application Diagram

Vs = 60V

Source resistance = 0.5

Ω

1ms < tr < 10ms

T = 400ms

t1 = 10s

Time

Vcc

Vs

10%

90%

tr

T

Figure 4. Load Dump Transient

Vs = 100V

Source resistance = 10

Ω

tr = 1

µs

T = 200

µs to 500µs

t1 = 200ms to 500ms

Time

Vcc

Vs

10%

90%

tr

T

t1

Figure 5. Inductive Switching Transient - Positive

L9909

5/9