LM9830VJD National Semiconductor, LM9830VJD Datasheet - Page 26

• Manufacturer Part Number: LM9830VJD
• Manufacturer: National Semiconductor

Specifications of LM9830VJD

• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 100
• Package Type: TQFP
• Lead Free Status / RoHS Status: Not Compliant

the 2 bit DAC, shown in Figure 17.
3.2 MicroStep Mode
Microstepping is a technique of driving the stepper motor with a
staircase approximation of a sine wave, as shown in Figure 18.
This technique maximizes the torque of a given motor, resulting in
a higher maximum speed. In addition, it increases the resolution
of the stepper motor. If a stepper motor moves 3.6° per full step,
microstepping can create positions inside the 3.6°: 1.8°, 0.9°, or
0.45°, for example. This increases the maximum vertical resolu-
tion of the scanner. Microstepping also results in quieter motor
movement.
The amplitude of the microstepped sine wave is controlled by the
output of the stepper motor DAC (Figure 19). The current in the
stepper motor winding is measured as a voltage across the sense
resistor, and the transistor drive signals are pulse width modu-
lated (PWM) to force the average current through the winding
equal to V
PWM, and Register 57 controls the minimum time the driver is on
every period. Register 57 should be set as short as possible, the
driver only needs to be on long enough to mask any transient
Starting from
a dead stop
Scanning
Stopped
Scan Mode
A
A
B
B
DAC
Figure 18: Bipolar Microstepping Waveform
/R
Figure 17: Full Step Current Control
SENSE
. Register 56 controls the frequency of the
0.5V for number of steps specified in
Kickstart Steps register (0-7). If
register is 0 there is no kickstart
current - movement begins at 0.35V.
0.35V
0.125V for number of steps specified
in Hold Current Timeout register
(0 - 31), 0V after time out. If register
is 0 there is no hold current.
DAC Voltage
1 microstep
26
noise generated by the driver transistor turning on.
Figure 20 shows the LM9830’s DAC voltages. The peak current
through the stepper motor winding will be 0.5V/R
index is incremented every microstep (StepSize pixel periods).
3.3 Pause Behavior - Non-Reversing Mode
When the Full Steps to Reverse When Buffer is Full register is
0, the stepper motor simply stops moving when the Pause signal
is received, as shown in Figure 21. The line of data currently
being processed (section “a” in Figure 21) will continue to be pro-
cessed and stored in SRAM. Additional lines may be digitized and
stored as well, depending on the number programmed in the
Lines to Process After Pause Scan Signal register (Figure 22).
This value is different for different scanner designs and should be
empirically set to the value that minimizes the spacial distortion
created by the motor slowing down and stopping.
MicroStep
DAC A
DAC B
Figure 19: Stepper Motor Waveform - LM9830 Signals
TR
Table Code
Pulse
A
A
B
B
Figure 20: Microstepping Current Control
-0
-1
-2
-3
-4
0
1
2
3
4
Figure 21: Stepper Motor Stopping
A (B)
Scanning
0
1
1
1
1
0
0
0
0
0
Pause
Signal
a
A (B)
0
0
0
0
0
0
1
1
1
1
b
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DAC Voltage
N/A
0.191V
0.353V
0.462V
0.500V
N/A
0.191V
0.353V
0.462V
0.500V
c
SENSE
. The table
d