UL
®
LSI/CSI
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747
SYNC
V
SS
HOME
PHA
INH1
PHB
PHC
INH2
PHD
ENABLE
RC
NC
LS8397
(631) 271-0400 FAX (631) 271-0405
April 2009
A3800
STEPPER MOTOR CONTROLLER
FEATURES:
• Controls Bipolar and Unipolar Motors
•
L297
operation with
added functions:
•
Selectable torque
ripple compensated phase drive
•
Selectable automated
switching between stepping and holding torques
•
Supply current < 400uA
• Half and full step modes
• Normal/wave drive
• Direction control
• Reset input
• Step control input
• Enable input
• PWM chopper circuit for current control
• Two over current sensor comparators with external references input
• All inputs and outputs TTL/CMOS compatible (TTL for 5V operation)
• 4.75V to 7V Operation (V
DD
– V
SS
).
•
LS8397
(DIP),
LS8397-S
(SOIC),
LS8397-TS
(TSSOP)
– See Figure 1 –
DESCRIPTION:
The
LS8397
Stepper Motor Controller generates four phase drive signal
outputs for controlling two phase Bipolar and four phase Unipolar mo-
tors. The outputs are used to drive two H-bridges for the two motor
windings in the Bipolar motor or the four driver transistors for the two
center- tapped windings in the Unipolar motor. The motor can be driven
in full step mode either in normal drive (two-phase-on) or wave drive
(one-phase-on) and half step mode. The
LS8397
provides two inhibit
outputs which are used to control the driver stages of each of the motor
phases. The circuit uses STEP, FRD/REV and HALF/FULL inputs in a
translator to generate controls for the output stages.
A dual PWM chopper circuit using an on-chip oscillator, latches and volt-
age comparators are used to regulate the current in the motor windings.
For each pair of phase driver outputs (PHA, PHB, and PHC, PHD) each
pulse of the common internal oscillator sets the latch and enables the
output. If the current in the motor winding causes the voltage across a
sense resistor to exceed the reference voltage, VREFs, at the compara-
tor inputs, the latch is reset disabling the output until the next oscillator
pulse.
Input for a separate reference voltage VREFh is also provided for reduc-
ing holding torque when the motor is not turning. When holding torque
mode is enabled with a resistor-capacitor pair connected to the RC Pin,
the sense comparator input reference switches between VREFs and
VREFh depending on whether the motor is turning or not. The separate
sense reference voltages allow for conserving power when the motor is
not turning. Holding torque mode can be disabled by connecting the RC
Pin to V
SS.
In the half-step stepping sequence, the phase drives alternate between
one-phase-on and two-phase-on in successive steps at full power thus
generating substantial ripple on the output torque. An input, CT_EN is
provided for selecting an operational mode in which the torque ripple is
corrected. In this mode the sense input reference voltage is switched to
100% and 70.7% of the applied voltages at the VREFs and VREFh in-
puts in successive one-phase-on and two-phase-on conditions, respec-
tively. The CONTROL input determines whether the chopper acts on the
8397-042109-1
PIN ASSIGNMENT
TOP VIEW
1
2
3
4
24
23
22
21
RESET
HALF/FULL
STEP
FWD/REV
OSC
VREFs
SENSE1
SENSE2
V
DD
CONTROL
VREFh
CT_EN
LSI
LS8397
5
6
7
8
9
10
11
12
20
19
18
17
16
15
14
13
FIGURE 1
phase driver outputs or the inhibit outputs. When the phase
lines are chopped, the non-active phase line of each pair
(PHA, PHB or PHC, PHD) is activated rather than de-
activating the active line to reduce dissipation in the load sens-
ing resistor Rs. Refer to Figure 5B for Bipolar motors. If PHA
is high and PHB is low, current flows through Q1, motor wind-
ing, Q4 and sense resistor Rs. When chopping occurs, PHB is
brought high and circulating current flows through Q1 and D3
and not through Rs resulting in less power dissipation in Rs.
Current decay is slow using this method. When the Control in-
put is brought low, chopping occurs by bringing INH1 low. In
this case circulating current flows through D2, motor winding
and D3 and through the power supply to ground causing the
current to decay rapidly. For Unipolar motors, only inhibit
chopping is used. Refer to Figure 6. When INH1 is brought
low the current flowing in either half of the center tapped mo-
tor winding recirculates through the diode across it.
INPUT/OUTPUT DESCRIPTION:
OSC Input
An RC input with the resistor connected to V
DD
and the capac-
itor connected to ground determines the oscillator chopper
rate. When connected as an oscillator, the oscillator output ap-
pears as a negative-going pulse at the Sync pin. If the oscillat-
ing pin is tied to ground, the Sync pin becomes an input.
Osc frequency, fosc = 1/0.69RC
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