l9909 STMicroelectronics, l9909 Datasheet - Page 5

• Manufacturer Part Number: l9909
• Description: Dc Motor Driver With Position Control
• Manufacturer: STMicroelectronics

Figure 3. L9909 Simplified Application Diagram
Figure 4. Load Dump Transient
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
Vs
Vcc
Vcc
Vs = 60V
Source resistance = 0.5 Ω
1ms < tr < 10ms
90%
10%
V
ERR
I
I
FB
COM
VFB
VCOM
T
tr
-
+
U709
-
+
M+
M-
T = 400ms
t1 = 10s
V
OUT
M
GND
Vcc
Time
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
Figure 5. Inductive Switching Transient - Positive
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.
Vs
Vcc
90%
10%
Vs = 100V
Source resistance = 10 Ω
tr = 1µs
T
tr
t1
T = 200µs to 500µs
t1 = 200ms to 500ms
L9909
Time
5/9