LS8297 Datasheet, PDF (1/8 Pages) LSI Computer Systems – STEPPER MOTOR CONTROLLER

LSI/CSI
LS8297
LS8297CT
U_{® L LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 [phone] FAX [phone]}
A3800
STEPPER MOTOR CONTROLLER
April 2009
FEATURES:
• Controls Bipolar and Unipolar Motors
• Cost-effective, low current, pin compatible replacement for L297
• Torque ripple compensated half-steps - LS8297CT
• 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)
• Supply current < 400uA
• 4.75 to 7V Operation (VDD – VSS).
• LS8297 (DIP), LS8297-S (SOIC), LS8297-TS (TSSOP)
LS8297CT (DIP), LS8297CT-S (SOIC), LS8297CT-TS (TSSOP)
– See Figure 1 –
DESCRIPTION:
The LS8297 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 LS8297 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, VREF, at the comparator
inputs, the latch is reset disabling the output until the next oscillator
pulse.
The CONTROL input determines whether the chopper acts on the
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 dis-
sipation in the load sensing resistors. Refer to Figure 5B for Bipolar mo-
tors. If PHA is high and PHB is low, current flows through Q1, motor
winding, 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 input 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
PIN ASSIGNMENT
TOP VIEW
SYNC 1
V SS 2
HOME ₃
PHA 4
INH1 5
PHB ⁶
PHC 7
INH2 8
PHD 9
ENABLE ¹⁰
20 RESET
19 HALF/FULL
18 _STEP
17 FWD/REV
16 OSC
15 ^VREF
14 SENSE1
13 SENSE2
12 V DD
11 CONTROL
FIGURE 1
current in either half of the center tapped motor winding recir-
culates through the diode across it.
LS8297CT is the torque ripple compensated version of the
LS8297. Torque imbalance resulting from alternating “one-
phase on”, “two-phase on” sequence of the half-step mode
(see Figure 4) is eliminated in the LS8297CT by switching the
sense reference voltage between 100% and 70.7% in alter-
nate steps.
INPUT/OUTPUT DESCRIPTION:
OSC Input
An RC input with the resistor connected to VDD and the ca-
pacitor connected to ground determines the oscillator chopper
rate. When connected as an oscillator, the oscillator output
appears as a negative-going pulse at the Sync pin. If the Os-
cillator pin is tied to ground, the Sync pin becomes an input.
Osc frequency, fosc = 1/0.69RC
SYNC
As an output the Sync can be used to drive Sync pins of other
LS8297s. This eliminates the need for RC components for
any other LS8297 controllers used in the system. As an input
the Sync can be driven by the LS8297 that has the RC oscilla-
tor components or by any other system external clock.
8297-042009-1